JP2006344407A - Composite dielectric material, prepreg using the same, metal foil painted object, molded compact, composite dielectric base board, multi-layered base board, and manufacturing method of composite dielectric material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite dielectric material realizing high relative dielectric constant εr, having high Q-value, having the relative dielectric constant with small temperature changing rate. <P>SOLUTION: The composite dielectric material contains dielectric ceramics and organic polymeric material. The dielectric ceramics contains powder of oxide having a composition expressed by general formula: (M, Li, Bi, RE)<SB>x</SB>TiO<SB>3</SB>, (wherein, M denotes at least one kind selected from Ba, Sr, and Ca; RE denotes at least one kind selected from La, Ce, Pr, Nd, Sm, Y, Yb, and Dy; and 0.9≤x≤1.05). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite dielectric material in which a dielectric ceramic and an organic polymer material are combined. Further, the present invention relates to a prepreg suitable for a circuit board material using such a composite dielectric material, a metal foil coated product, a molded product, a composite dielectric substrate, and a multilayer substrate. Furthermore, the present invention relates to a method for manufacturing such a composite dielectric material.

  For example, in the information communication field, the use frequency band tends to shift to a high frequency, and high frequency in the gigahertz (GHz) band is used in mobile communication such as satellite broadcasting, satellite communication, mobile phone and car phone. Yes.

  In circuit boards and electronic components mounted on devices used in the high frequency band as described above, the dielectric material to be used needs to be a low loss material having high Q and excellent high frequency transmission characteristics. Furthermore, in order to achieve high performance and miniaturization of circuit boards and electronic components, a dielectric material having a high relative dielectric constant εr in the used frequency band is required. In particular, the point of miniaturization is based on the principle that the wavelength of the electromagnetic wave in the dielectric material is shortened by 1 / √εr, and the smaller the dielectric material having a higher relative dielectric constant εr, the smaller the circuit board or electronic component. Is possible. In addition, since there is a demand for a substrate having a capacitor function, a high dielectric constant substrate using such a dielectric material is also required.

  Dielectric ceramics, which are inorganic materials, are widely used as dielectric materials, and dielectric ceramics having various compositions according to required characteristics have been developed. However, when the dielectric ceramic is used for a circuit board or an electronic component, it is generally used in the form of a bulk sintered body, and since firing at a high temperature is necessary, there is a problem that the application range is restricted. is there. In addition, shrinkage and deformation that occur in the baking process at high temperatures, and further deterioration of characteristics due to oxidation of the internal conductor, for example, become a problem.

  Under such circumstances, a composite dielectric material in which a dielectric ceramic powder and an organic polymer material are combined has been proposed (see, for example, Patent Document 1 and Patent Document 2). Since composite dielectric materials do not require firing at high temperatures, they can be used in a wide range of applications. Shrinkage and deformation during the firing process, one of the manufacturing processes for bulk sintered bodies, and deterioration of internal conductor properties There is no problem. In addition, since the organic polymer material is contained, the degree of freedom of shape workability is increased, the weight is light, and the relative permittivity εr and the like can be arbitrarily changed depending on the blending ratio of the dielectric ceramic powder.

For example, the invention described in Patent Document 1 discloses a composite dielectric in which a ceramic such as a BaTiO ₃ system is dispersed in a resin (polyvinyl benzyl ether compound). In the invention described in Patent Document 1, a relative dielectric constant of 10 or more is realized in a high frequency band of 10 MHz or more by setting the ceramic content to 30% by volume or more.

On the other hand, Patent Document 2 relates to a composite material for a dielectric electromotive force antenna, and a dielectric ceramic having a positive relative dielectric constant temperature change characteristic and a dielectric ceramic having a negative relative dielectric constant temperature change characteristic. In addition, a composite material for a dielectric electromotive force antenna is disclosed in which a polymer material is mixed so that the temperature change of the relative dielectric constant is ± 50 ppm / ° C. or less.
JP 2001-181027 A JP-A-4-161461

  By the way, as characteristics required for the composite dielectric material, in addition to a high relative dielectric constant εr, a high Q value as an index of loss, a low temperature coefficient, and the like can be mentioned. And in order to implement | achieve the further performance improvement of a circuit board or an electronic component, it is necessary for the composite dielectric material to be used to satisfy | fill all these characteristics.

  From this point of view, for example, it is difficult to obtain a high Q value while realizing a high relative dielectric constant εr, and further to reduce the absolute value of the temperature coefficient τε of the relative dielectric constant εr. The fact is that the characteristics of this must be sacrificed. For example, in the invention described in Patent Document 1, a certain degree of relative permittivity εr is obtained, but the Q value and the temperature coefficient τε are not studied. In the invention described in Patent Document 2, the temperature coefficient is emphasized, and the relative dielectric constant εr is 10 or less in any sample. The Q value has not been studied. For example, a low-loss dielectric material having a high Q is required for an antenna or the like where gain is important, and improvement thereof is desired.

  The present invention has been proposed in view of the above circumstances. That is, an object of the present invention is to provide a composite dielectric material that realizes a high relative dielectric constant εr, has a high Q value, and has a small temperature change rate of the relative dielectric constant. In addition, the present invention utilizes the improvement in characteristics of the composite dielectric material, for example, a prepreg, a metal foil coated product, a molded body, and a composite dielectric that can improve performance when used for a circuit board, for example. An object is to provide a body substrate and a multilayer substrate. Furthermore, an object of the present invention is to provide a method for producing a composite dielectric material that exhibits excellent fluidity and is easy to produce, for example, a circuit board.

As a result of intensive studies over a long period of time in order to solve the above-mentioned problems, the present inventors have a positive temperature characteristic τε by allowing Li and rare earth elements to be contained simultaneously in so-called A sites in titanate. Focusing on the fact that the titanate such as BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , Li _1/2 RE _1/2 TiO ₃ (RE is a rare earth element) is dissolved in an appropriate ratio, the basic In particular, we have developed an oxide that consists of an oxide dielectric having a single-phase perovskite structure and exhibits good values in a well-balanced manner for each of the dielectric constant, Q characteristic, and temperature characteristic. As a result of further research, this system has the best characteristics when using La, which has the largest ionic radius, as the rare earth element RE. However, when Bi, which has an ionic radius close to La, is used instead of La, the dielectric constant is even higher. The inventor has obtained knowledge that materials having ε, Q characteristics, and temperature characteristics can be obtained. As a result of further investigation, this material is used as a dielectric ceramic in combination with an organic polymer material in a composite dielectric material, so that the dielectric constant, the Q characteristic, and the temperature characteristic exhibit good values with good balance. The knowledge that a composite dielectric material can be obtained has been obtained, and the present invention has been completed.

That is, the composite dielectric material according to the present invention is a composite dielectric material containing a dielectric ceramic and an organic polymer material, and the dielectric ceramic is represented by the general formula (M, Li, Bi, RE) _x. TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents at least one selected from La, Ce, Pr, Nd, Sm, Y, Yb, and Dy. 0.9 ≦ x ≦ 1.05)), and an oxide powder having a composition represented by:

The oxide powder used as the dielectric ceramic in the composite dielectric material contains Li _1/2 Bi _1/2 TiO ₃ , Li _1/2 RE _1/2 TiO ₃ (RE is a rare earth element). The temperature characteristic τε of the dielectric constant εr becomes flat. Further, by including, for example, Ba, Sr, Ca, etc. as M in the formula, a high relative dielectric constant εr is shown. Of these Ba, Sr, and Ca that cause the high relative dielectric constant εr, in particular, Ca has a high Qf value, and Ba and Sr have a high relative dielectric constant εr that exceeds Ca. Therefore, for example, by blending Sr or Ba with Ca, an oxide powder having both high Q characteristics and high relative dielectric constant εr is realized.

  In the present invention, as described above, oxide powder having a good balance of relative dielectric constant εr, temperature characteristic τε and Q characteristic is used as the dielectric ceramic. By compounding the oxide powder with an organic polymer material, for example, a composite dielectric material having a high relative dielectric constant εr and Q characteristic and a small temperature characteristic τε of relative dielectric constant εr is realized.

In addition, the method for producing a composite dielectric material according to the present invention includes a firing step for obtaining a fired product by holding the raw material composition at a predetermined firing temperature, and a grinding step for grinding the fired product using an airflow pulverizer. And general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, Pr, Nd, Sm, Y) , Yb, Dy, and 0.9 ≦ x ≦ 1.05), and a dielectric including the oxide powder is prepared. It is characterized by mixing a body ceramic and an organic polymer material.

  Oxidation with a very fine powder content is suppressed by using an air-flow type pulverizer to produce dielectric ceramics, which suppresses the generation of extremely fine powder compared to other pulverizers. A product powder is obtained. When such an oxide powder is used as a dielectric ceramic, good fluidity is exhibited in a mixture mixed with an organic polymer material, and for example, manufacture of a circuit board is facilitated.

According to the present invention, the general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, Pr, Nd, And at least one selected from Sm, Y, Yb, and Dy, and 0.9 ≦ x ≦ 1.05). For example, a composite having a high dielectric constant εr of 10 or more, a high Q value exceeding 200, and a temperature coefficient of change of the dielectric constant εr within ± 250 ppm. It is possible to provide a dielectric material.

  In addition, according to the present invention, a high-performance prepreg, a metal foil coated product, by using a composite dielectric material that is excellent with respect to each characteristic of the relative dielectric constant εr, the Q value and the temperature change rate of the relative dielectric constant εr, Molded bodies, composite dielectric substrates, and multilayer substrates can be provided.

Furthermore, according to the present invention, the general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, Pr, Represents at least one selected from Nd, Sm, Y, Yb, and Dy, and 0.9 ≦ x ≦ 1.05). By using the type pulverizer, a composite dielectric material excellent in any of the dielectric constant εr, the Q characteristic, and the temperature change rate of the dielectric constant εr can be easily manufactured.

  Hereinafter, a composite dielectric material according to the present invention and a prepreg, a metal foil coated product, a molded body, a composite dielectric substrate, a multilayer substrate, and a method for producing the composite dielectric material using the same will be described in detail.

  The composite dielectric material of the present invention is a composite of dielectric ceramics and an organic polymer material (resin). Here, first, examples of the organic polymer material combined with the dielectric ceramic include thermoplastic resins and thermosetting resins. Any resin may be selected from these resins depending on the desired properties. For example, as the thermoplastic resin, polypropylene resin, polystyrene resin, polyetherimide resin, polyethersulfone resin, Examples thereof include polyacetal resins, cyclopentadiene resins, liquid crystal polymers, and mixtures thereof. The thermoplastic resin is a resin group having a relatively low loss (high Q) in a high frequency range.

  Examples of thermosetting resins include phenol resins, epoxy resins, unsaturated polyester resins, vinyl ester resins, polyimide resins, maleimide resins, polyphenol polycyanate resins, vinyl benzyl resins, and mixtures thereof. Can be mentioned. These resins are also a resin group having a relatively low loss (high Q) in a high frequency range, but when a thermosetting resin is used, a composite dielectric material having excellent heat resistance in a soldering process or the like is obtained. In particular, a vinyl benzyl resin such as a polyvinyl benzyl ether compound is a material having a dielectric property that does not depend on temperature and hygroscopicity and excellent heat resistance. In addition, when hardening a thermosetting resin, you may make a hardening | curing agent exist, for example, well-known radical polymerization initiators, such as a benzoyl peroxide, a methyl ethyl ketone peroxide, a dicumyl peroxide, can be used.

On the other hand, as dielectric ceramics, the general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, Pr, Nd, Sm, Y, Yb, Dy is used, and an oxide powder having a composition represented by 0.9 ≦ x ≦ 1.05 is used. This oxide powder is made of a titanate such as BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , Li _1/2 RE _1/2 TiO ₃ (RE is a rare earth element), Li _1/2 Bi _1/2 TiO ₃ or the like. It is an oxide dielectric powder having a perovskite structure in solid solution.

In the oxide represented by the general formula (M, Li, Bi, RE) _x TiO ₃ , the ratio x of M, Li, Bi, and RE is set to 0.9 to 1.05. In the above general formula, x is basically 1, but sometimes x takes a value other than 1, that is, deviates from the stoichiometric composition. Therefore, in the present invention, x is set to the above range in order to define the degree of deviation from the allowable stoichiometric composition.

The basic composition of the oxide represented by the general formula (M, Li, Bi, RE) _x TiO ₃ is aBaTiO ₃ —bSrTiO ₃ —cCaTiO ₃ —dLi _1/2 Bi _1/2 TiO ₃ —eLi _1/2. RE _1/2 TiO ₃ [wherein RE represents at least one selected from La, Ce, Pr, Nd, Sm, Y, Yb, and Dy, and a to e represent the blending ratio (mol%) of each component. To express. ]. Each component preferably satisfies the following conditions.
0 ≦ a ≦ 5
0 ≦ b ≦ 20
10 ≦ c ≦ 45
a + b + c ≦ 50
b + d / 2 ≦ 33
c + d / 2 ≦ 65
a + b + c + d + e = 100

The reason for limiting the composition of each component in the basic composition component will be described. First, BaTiO ₃ has an effect of improving the relative dielectric constant εr, but when the mixing ratio a of BaTiO ₃ exceeds 5 mol%, The Q characteristic (Qf value) is significantly reduced. Therefore, the blending ratio a of BaTiO ₃ is preferably 5 mol% or less. The mixing ratio a of BaTiO ₃ may be zero in some cases.

Next, a blending ratio b of SrTiO _3, SrTiO ₃ also has the effect of improving the dielectric constant .epsilon.r. When the blending ratio b of SrTiO ₃ exceeds 20 mol%, the Q characteristic is remarkably deteriorated. Therefore, the blending ratio b of SrTiO ₃ is preferably 20 mol% or less. The blending ratio b of SrTiO ₃ may be zero depending on circumstances.

Since CaTiO ₃ has the highest Qf value (13000 GHz) and a relatively high relative dielectric constant εr (170) of each unit material, it is effective in improving the Q characteristics. , Has the effect of producing a certain high value. However, if there is too much CaTiO ₃ , the temperature characteristic τε of the dielectric constant may be deteriorated. Therefore, from these viewpoints, the CaTiO ₃ blending ratio c is preferably 10 mol% or more and 45 mol% or less. If the blending ratio c of CaTiO ₃ exceeds 45 mol%, the temperature characteristic τε may be deteriorated. If the mixing ratio c of CaTiO ₃ is less than 10 mol%, there is a possibility that Qf value decreases.

  Further, regarding the titanate of these alkaline earth metals (Ba, Sr, Ca), it is necessary to consider the total amount (a + b + c). Since all of the titanates of Ba, Sr, and Ca show a negative dielectric constant temperature characteristic τε, if the total amount (a + b + c) is too large, the absolute value of the temperature characteristic τε increases in the negative direction. Therefore, the total amount (a + b + c) needs to be 50 mol% or less. Conversely, if the total amount (a + b + c) is too small, the relative dielectric constant εr and the Q characteristics may be degraded. For this reason, the total amount (a + b + c) is preferably 20 mol% or more.

Li _1/2 Bi _1/2 TiO ₃ has a stronger function of controlling the temperature characteristic τε than Li _1/2 RE _1/2 TiO ₃ , but the deterioration of the Q characteristic is also Li _1/2 RE _1/2 TiO _3. More intense. Therefore, the blending ratio d may be set in consideration of the temperature characteristic τε of the composite dielectric material. However, if the blending ratio d is too large, the Q characteristic is deteriorated, and if it is too small, the relative permittivity εr is low. Therefore, the content is preferably 5 mol% or more and 50 mol% or less.

Further, Li _1/2 RE _1/2 TiO ₃ mainly contributes to control of the temperature characteristic τε of the composite dielectric material, and the temperature characteristic τε is improved as the blending ratio e is increased, but the relative dielectric constant is increased. εr and Q characteristics are reduced. On the other hand, if the blending ratio e is too small, the absolute value of the temperature characteristic τε in the minus direction increases. Therefore, the blending ratio e of Li _1/2 RE _1/2 TiO ₃ is preferably 3 mol% or more and 75 mol% or less.

  On the other hand, b + d / 2 represents the total amount of Sr and Bi in the basic composition. When the total amount (b + d / 2) of Sr and Bi is excessive, the Q characteristic is deteriorated. Therefore, b + d / 2 needs to be 33 mol% or less. In addition, if the total amount of Sr and Bi is too small, the absolute value of the temperature characteristic may increase to the minus side, and therefore b + d / 2 is preferably set to 10 mol% or more.

  C + d / 2 represents the total amount of Ca and Bi in the basic composition. When the total amount (c + d / 2) of Ca and Bi becomes excessive, the temperature characteristic τε is deteriorated. Therefore, c + d / 2 needs to be 65 mol% or less. Moreover, since there exists a possibility that Q characteristic may fall when there is too little total amount of Ca and Bi, it is preferable that c + d / 2 shall be 15 mol% or more.

In the oxide powder, among the basic composition components, in Li _1/2 RE _1/2 TiO ₃ , RE is preferably Nd, and further, a part thereof is a lanthanide group element (La, And at least one selected from Ce, Pr, Sm, Y, Yb, and Dy). By setting RE to Nd, the dielectric constant ε, the Q characteristic and the temperature characteristic are well balanced, and the balance between the characteristic and the material cost is also good. Further, by substituting a part of Nd with an element having an ionic radius larger than Nd, such as La, Ce, or Pr, the relative dielectric constant εr can be further increased. By replacing a part of Nd with an element having an ion radius smaller than Nd, such as Sm, Y, Yb, or Dy, the Qf value can be increased.

By the way, the specific surface area of the oxide powder used as the dielectric ceramic affects the fluidity of the mixture after being mixed with the organic polymer material. When the specific surface area of the oxide powder is reduced, the fluidity of the mixture is improved, and the Q characteristics are improved, for example, the moldability is improved when manufacturing a substrate or the like, and the manufacturing is facilitated. . From such a viewpoint, the specific surface area (SSA) of the oxide powder is preferably 9 m ² / cm ³ or less.

  In addition, the specific surface area in this invention is converted into the value per unit volume based on following formula (1), in order to compare the particle | grains (powder) from which a density differs.

SSA (m ² / cm ³ ) = SSA (m ² / g) × ρ (g / cm ³ ) (1)
SSA (m ² / g): Specific surface area of particles measured by BET method ρ: Density of particles measured using specific gravity bottle

  In the composite dielectric material of the present invention, there is no particular limitation on the particle size of the oxide powder, but it is preferable to select appropriately in view of mixing with the organic polymer material. For example, if the particle size of the dielectric ceramic used is too small, kneading with the organic polymer material may be difficult. On the other hand, when the particle size of the dielectric ceramic becomes too large, the mixed state with the organic polymer material becomes non-uniform and the dielectric characteristics may become non-uniform. Further, when the content of dielectric ceramics is large, there is a possibility that a dense composite dielectric material cannot be obtained. Considering these matters, the average particle diameter of the oxide powder used as the dielectric ceramic is preferably 0.2 μm or more and 100 μm or less.

Hereinafter, a method for manufacturing the composite dielectric material having the above-described configuration will be described. First, a general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, and Pr used as dielectric ceramics). , Nd, Sm, Y, Yb, Dy, and 0.9 ≦ x ≦ 1.05).

  When producing the oxide powder, first, a predetermined amount of the main component raw material powder is weighed and mixed to obtain a raw material composition. As the raw material powder of the main component, oxide powders and compounds that become oxides upon heating, such as carbonates, hydroxides, oxalates, nitrates, and the like can be used. In this case, not only one kind of metal oxide (compound) but also a composite oxide powder containing two or more kinds of metals may be used as the raw material powder. Moreover, a temporarily fired product can be used as a raw material composition. The calcined product is obtained by calcining the raw material powder weighed so as to have a final composition at a predetermined temperature. In addition, subcomponents, such as an additive, are added to a temporary baked material, and it is good also as a raw material composition. What is necessary is just to select the average particle diameter of each raw material powder suitably in the range of 0.1 micrometer-3.0 micrometers, for example.

  Next, a firing step for firing the raw material composition is performed. The firing temperature and holding time may be appropriately set according to the composition of the oxide powder.

  After the firing step, a pulverization step is performed. The oxide powder is obtained by pulverizing the fired product obtained in the firing step.

  By the way, in general, the particle size of the powder (pulverized product) obtained by pulverization is non-uniform, and the pulverized product includes extremely fine powder. When, for example, a ball mill or the like is used when producing the oxide powder, the ultrafine powder is repeatedly pulverized, so that the pulverized product contains a relatively large amount of ultrafine powder. Increases surface area. As a result, when the oxide powder that is a pulverized product and the organic polymer material are mixed, the fluidity of the mixture may be deteriorated.

  Therefore, in the present invention, it is preferable to use an airflow pulverizer as the pulverizer. Since an airflow type pulverizer generally has a classification function, excessive pulverization of ultrafine powder can be suppressed. In the pulverization step, coarse pulverization may be performed prior to pulverization (fine pulverization) using an airflow pulverizer.

  As described above, the oxide powder as the dielectric ceramic can be obtained by performing the firing step and the grinding step once. However, in the present invention, after the first firing and grinding, the firing and grinding are performed again. Preferably it is done. That is, it is preferable to repeat the firing step and the pulverization step. The specific surface area of the finally obtained oxide powder can be reduced, and the fluidity of the mixture mixed with the organic polymer material can be improved. As a result, it is easy to manufacture a substrate or the like using the composite dielectric material, and it is possible to improve the Q characteristic and the like.

  In addition, when the firing process and the pulverization process are repeated, the firing temperature in the first firing process is set to a relatively high temperature from the viewpoint of further improving the dielectric properties, and the firing temperature in the second and subsequent firing processes is set to that. A lower temperature is preferable.

  Thus, when controlling a calcination temperature, the calcination temperature in the 1st baking process can be set to comparatively high temperature. The firing temperature in the first firing step may be appropriately set according to the composition of the oxide powder, and can be set to 1100 ° C. to 1300 ° C., for example. The holding time may be appropriately set according to the composition of the oxide powder.

  In the second and subsequent firing steps, the firing temperature is set lower than the firing temperature in the first firing step. The firing temperature in the second and subsequent firing steps may be lower than that in the first firing step, and may be, for example, 1050 ° C. to 1250 ° C. The holding time may be appropriately set according to the composition of the oxide powder.

For example, in the first firing step, when firing is performed at a relatively high temperature as described above, the pulverized product obtained by pulverization contains a large amount of ultrafine powder. The reason why an extremely fine powder is likely to be generated is that a fired product obtained by high-temperature firing is hard and excessive energy is required for pulverization. As a result of containing a large amount of ultrafine powder in the pulverized product, the specific surface area of the obtained pulverized product (oxide powder) greatly exceeds 9 m ² / cm ³ and the fluidity deteriorates when mixed with the organic polymer material. May be incurred. Even when an airflow type pulverizer is used at the time of pulverization, it is difficult to eliminate such an increase in specific surface area.

Therefore, after the first pulverization step, the second firing is performed at a relatively low firing temperature. By firing again at a low temperature, the ultrafine oxide powder generated in the first pulverization step is integrated into an oxide powder having a larger particle size. In the second pulverization step, the integrated baked product is pulverized again, but since the second baking temperature is relatively low, the hardness of the baked product obtained in the second calcination step is the first time. It can be pulverized with relatively low energy. Therefore, in the second pulverization, generation of ultrafine powder is suppressed, and for example, an oxide powder having a specific surface area of 9 m ² / cm ³ or less can be easily obtained. A higher effect can be obtained by further repeating the firing step and the pulverization step.

  At this time, it is preferable that the difference between the firing temperature in the first firing step and the firing temperature in the second and subsequent firing steps is 50 ° C. or more. When the difference in firing temperature is less than 50 ° C., there is a fear that the specific surface area is lowered and the effect of improving the Q characteristic is insufficient. More preferably, the difference between the firing temperature in the first firing step and the firing temperature in the second and subsequent firing steps is 100 ° C. or higher.

Furthermore, when repeating a baking process and a grinding | pulverization process, it is preferable to make the calcination temperature in the baking process performed last higher than the temperature range which a pyrochlore phase produces | generates in oxide powder. The oxide powder having a composition represented by the general formula (M, Li, Bi, RE) _x TiO ₃ used in the present invention generates a pyrochlore phase that causes a decrease in dielectric properties as compared with the case where Bi is not contained. It has the problem of being easy to do. Thus, by controlling the firing temperature in this way, an oxide powder having a substantially single-phase perovskite structure can be obtained. By using this oxide powder as a dielectric ceramic, it is possible to further improve the dielectric characteristics of the composite dielectric material.

In the composite dielectric material of the present invention, the dielectric ceramic containing the oxide powder represented by the general formula (M, Li, Bi, RE) _x TiO ₃ and the organic polymer material (resin) are mixed. Can be obtained. At this time, the mixing ratio of the dielectric ceramics can be arbitrarily set, but is preferably 20% by volume or more and less than 70% by volume. The mixing ratio of the organic polymer material is 30% by volume or more and less than 80% by volume. If the ratio of the dielectric ceramic is less than 20% by volume, the effect of containing the oxide having a high relative dielectric constant εr may not be sufficiently exhibited. On the contrary, when the ratio of the dielectric ceramic becomes 70% by volume or more, the density of the obtained composite dielectric material is deteriorated, and there is a possibility that problems such as deterioration of dielectric characteristics due to easy penetration of moisture, for example. is there.

  Further, when mixing the dielectric ceramic powder and the organic polymer material, it is preferable to set the blending in consideration of the relative dielectric constant εr of the finally obtained composite dielectric material. Specifically, the blending ratio is preferably adjusted so that the relative dielectric constant εr in the microwave region of the composite dielectric material is 10 or more, and the ratio of the dielectric ceramic powder is 40% by volume or more and 70% by volume. More preferably, it is less than%. As a result, the dielectric properties of the oxide powder used as the dielectric ceramic can be sufficiently exhibited in the composite dielectric material.

  Unlike the bulk sintered body made only of dielectric ceramics, the composite dielectric material of the present invention is constituted by compositing dielectric ceramic powder with an organic polymer material. Therefore, the specific gravity can be reduced and the weight of the material can be reduced. Further, since the composite dielectric material can be produced at a low temperature of about 200 ° C., shrinkage or deformation caused by firing at a high temperature is not observed, and deterioration of the characteristics of the internal conductor made of, for example, silver or copper can be prevented.

  The composite dielectric material having the above configuration can be used for, for example, a circuit board, a prepreg for a circuit board, various electronic components, and the like. For example, when used for a circuit board, a high-frequency circuit board is constructed by using the composite dielectric material for a so-called base board, forming a wiring pattern thereon, and mounting necessary components. Can do. Further, a multilayer substrate can be formed by laminating a plurality of layers of substrates made of the composite dielectric material. For example, a high-performance multilayer substrate can be constructed by using the composite dielectric material as a prepreg and laminating a substrate made of the composite dielectric material through the prepreg.

  Hereinafter, a prepreg, a metal foil coated product, a molded product, and a composite dielectric substrate and a multilayer substrate using these will be described as usage forms of the composite dielectric material of the present invention.

  First, a preferred method for producing a prepreg will be described. In order to produce a prepreg, for example, a polyvinyl benzyl ether compound is used as an organic polymer material, and a 40 to 60% solution is prepared in terms of mass percentage. The solvent used at this time is preferably a volatile solvent such as toluene, xylene or methyl ethyl ketone. Thereafter, the dielectric ceramic powder is added and mixed with a mixing stirrer. Mixing can also be performed with a ball mill or the like. Finally, a volatile solvent such as toluene is added to adjust the viscosity, and the mixture is stirred with a mixing stirrer for 10 to 20 minutes. At this time, it is desirable to stir while degassing. Thereby, a composite dielectric substrate material composition solution (slurry) can be obtained.

The composite dielectric material composition solution (slurry) thus obtained is applied to a cloth substrate such as a glass cloth. In particular, it is preferable to use a glass cloth as the cloth substrate. A glass cloth having a cloth mass of 40 g / m ² or less and a thickness of 50 μm or less (for example, trade name Asahi Schwer, etc.) is preferable for improving the filling rate of the dielectric ceramic powder. Although there is no restriction | limiting in particular in the minimum of cloth mass and the minimum of thickness, They are about 25 g / m < ² > and 30 micrometers, respectively.

  As the glass cloth, an E glass cloth, a D glass cloth, an H glass cloth, or the like can be properly used according to electrical characteristics. Further, for the purpose of improving interlayer adhesion, etc., a coupling treatment or the like may be performed on the glass cloth. In addition to the glass cloth, the cloth base material may be a reinforcing material using a nonwoven fabric such as aramid or polyester woven from yarn. In this case, the thickness or the like may be the same as that of the glass cloth.

  As the coating thickness at the time of the coating, it is practically preferable to set the thickness after the B-stage to 50 to 200 μm, but it is possible to select the coating timely according to the plate thickness and filler content. . Further, the coating method may be any known method such as a method of applying a predetermined thickness with a vertical coating machine, a method of applying to a cloth substrate by a doctor blade coating method, etc. A production method can be selected according to the method. For this reason, productivity is high. A film formed by such a method is heat-treated at 100 to 120 ° C. for 0.5 to 3 hours to obtain a prepreg (B stage). The conditions at this time may be selected as appropriate depending on the resin content, desired fluidity, and the like.

The case where a prepreg obtained here is used to produce a double-sided copper foil substrate, for example, will be described. The prepreg is stacked so as to have a predetermined thickness, and both sides of the laminate are sandwiched between copper foils and molded. The forming method is performed by a known method such as hot pressing. The molding conditions are preferably 100 to 200 ° C., 9.8 × 10 ^{5 to} 7.8 × 10 ⁶ Pa, 0.5 to 10 hours, and may be step-cured as necessary.

  The metal foil used at this time is generally copper, but is not limited thereto, and can be selected from gold, silver, aluminum, and the like. In addition, it is preferable to use an electrolytic foil when securing peel strength, and using a rolled foil with less skin effect due to surface irregularities when emphasizing high-frequency characteristics. The thickness of the metal foil is 8 to 70 μm, and a metal foil having an appropriate thickness may be selected and used according to the application and required characteristics (pattern width and accuracy, DC resistance, etc.).

  In addition, the above-mentioned composite dielectric material composition solution may be coated on a metal foil such as a copper foil as described above by a doctor blade coating method or the like and dried to obtain a metal foil coated product. A composite dielectric substrate may be produced. The coating thickness in this case may be the same as that of the prepreg. Drying may be performed at 100 to 120 ° C. for about 0.5 to 3 hours.

Moreover, when producing a plate-shaped molded object by press molding, although the mixing method etc. are the same as the method mentioned above, the mixed slurry is dried at 90-120 degreeC, and the lump of a mixture is produced. Furthermore, this lump is pulverized by a mortar or a known method to obtain a mixed powder. This mixed powder is press-molded in a mold at 100 to 150 ° C., 9.8 × 10 ^{5 to} 7.8 × 10 ⁶ Pa, for 0.1 to 3 hours to obtain a plate-shaped molded body. The thickness of the plate-shaped molded body is preferably 0.05 to 5 mm, and is appropriately selected according to the desired plate thickness and dielectric ceramic powder content. The molded body is cured at 100 to 200 ° C., 9.8 × 10 ^{5 to} 7.8 × 10 ⁶ Pa, for 0.5 to 10 hours. Further, step cure may be performed as necessary.

A composite made by appropriately combining the prepreg produced as described above, a metal foil coated product such as copper foil, a plate-shaped molded body, a metal foil such as copper foil, and a cloth base material such as glass cloth. A dielectric substrate is produced. The molding conditions are 100 to 200 ° C., 9.8 × 10 ^{5 to} 7.8 × 10 ⁶ Pa, and 30 to 120 minutes. Alternatively, the prepreg, metal foil coated product, molded product, metal foil such as copper foil, cloth base material such as glass cloth, etc., and composite dielectric substrate produced by these, etc. are used as laminated elements, and in multiple layers It is also possible to construct a multilayer substrate by stacking layers.

  In addition to the above, the composite dielectric material of the present invention can be used for various electronic components such as multilayer capacitors, resonators, inductors, and antennas. For example, in the case of a resonator, a strip line, a ground plane, an external conductor, an internal conductor, or the like may be formed between the surface of the laminate made of the composite dielectric material or between the laminates, and the necessary portions may be electrically connected. . The resonator using the composite dielectric material of the present invention is used in various filters such as a high-pass filter, a low-pass filter, a band-pass filter, a band elimination filter, a demultiplexing filter, a diplexer, a voltage-controlled oscillator, etc. that combine these filters. Application is possible. The composite dielectric substrate and multilayer substrate of the present invention are suitable for use in a high frequency band of 500 MHz or higher. When the composite dielectric material of the present invention is used for these electronic components, the temperature change coefficient τε of the relative dielectric constant εr is adjusted according to the usage environment by adjusting the mixing ratio of the dielectric ceramics and the organic polymer material. It is also possible to control.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

<Production of composite dielectric material>
Dielectric ceramics (average particle diameter: 2.5 μm to 3.6 μm) so that the volume ratio of the dielectric ceramic powder and the organic polymer material (polyvinylbenzyl ether compound) is a predetermined ratio (dielectric ceramic powder 40% by volume). ) And the polyvinylbenzyl ether compound were weighed and mixed thoroughly in toluene. This was dried at 110 ° C. and then pulverized to obtain a mixed powder of dielectric ceramic and polyvinyl benzyl ether compound. This powder was put in a mold and thermally cured at 200 ° C. to produce a plate-shaped composite dielectric. Then, a rod-like sample (1 mm × 1 mm × 9 mm) was cut out and used as a measurement sample.

<Evaluation>
About each produced sample, the relative dielectric constant εr and Q at 2 GHz are set to 20 ° C. by the cavity resonator perturbation method (measurement device used: manufactured by Hewlett-Packard Co., Ltd., trade names: 83620A and 8757C, and 900 series manufactured by a constant temperature bath despatch). Measured with Further, the relative dielectric constant εr was measured in the temperature range of −30 ° C. to + 85 ° C. to obtain the temperature characteristic τε.

<Experiment 1: Examination of composition of dielectric ceramics>
First, dielectric ceramics used for the composite dielectric material were produced as follows.
As raw powders, LiCO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , Bi ₂ O ₃ , La (OH) ₃ , Nd (OH) ₃ , Sm (OH) ₃ , TiO _{2, and the} like were prepared. These raw material powders were weighed to a predetermined value at a predetermined molar ratio and mixed for 16 hours using a wet ball mill. This mixture was held at 1000 ° C. for 2 hours and pre-baked. After the calcination, the obtained calcination product was pulverized for 16 hours using a wet ball mill, and the obtained pulverization product was used as a raw material composition.

  Next, the baking process was performed. In this firing step, a heat treatment was performed in which the raw material composition (pulverized product) was held at 1190 ° C. for 4 hours. After the firing step, a pulverization step was performed. In the pulverization step, the fired product was coarsely pulverized using a mortar until it passed through a mesh having an opening of 1 mm, and then finely pulverized using an airflow pulverizer.

After finishing the pulverization step, a second baking step, a second pulverization step, a third calcination step, and a third pulverization step were sequentially performed. That is, the pulverization step and the firing step were repeated three times. The firing conditions in the second and subsequent firing steps were a firing temperature of 1080 ° C. and a holding time of 2 hours. According to the above procedure, an oxide powder represented by the general formula (M, Li, Bi, RE) _x TiO ₃ used as the dielectric ceramic powder was obtained.

Using the obtained oxide powder as dielectric ceramics, Samples 1 to 38 shown in Table 1 and Samples 39 to 45 shown in Table 2 were prepared according to the description relating to the production of the composite dielectric material. The oxide powder used in Sample 45 is a mixture obtained by adding an additive (SiO ₂ or the like) shown in Table 1 to a pre-baked material mainly composed of titanate as a raw material composition. . Tables 1 and 2 show the composition of the oxide powder used as the dielectric ceramic.

  And about these samples, the dielectric property was evaluated. The results are shown in Table 1 and Table 2 together.

As is clear from Tables 1 and 2, the oxide ceramics (sample 1 to sample 42) represented by the general formula (M, Li, Bi, RE) _x TiO ₃ are used as the dielectric ceramics. Balanced characteristics are obtained in all of the dielectric constants εr, Qf and the temperature characteristic τε. On the other hand, in the samples 43 to 45 not containing the rare earth elements RE and Bi, the Qf or the temperature characteristic τε is greatly deteriorated.

Samples 1 to 38 shown in Table 1 each have a basic composition represented by aBaTiO ₃ —bSrTiO ₃ —cCaTiO ₃ —dLi _1/2 Bi _1/2 TiO ₃ —eLi _1/2 RE _1/2 TiO _3. Oxide powders whose components are within the preferred range are used as dielectric ceramics, and all these samples have a high relative dielectric constant εr exceeding 10, a Qf of 200 or more, and a temperature characteristic τε within ± 250 ppm / ° C. Has been achieved. Thus, it can be seen that a composite dielectric material exhibiting excellent dielectric properties can be realized by setting each component in the basic composition within a preferable range.

<Experiment 2: Examination of firing temperature of dielectric ceramics>
In Experiment 2, the composition of the oxide powder used in Sample 6 of Experiment 1 was taken as an example, and the optimum firing temperature of the oxide powder was examined.

  First, the temperature range in which the pyrochlore phase was generated was confirmed. A raw material composition was prepared in the same manner as in Experiment 1, and this raw material composition was subjected to a firing step. In the firing step, the raw material composition was held at 1190 ° C. for 4 hours. After the firing step, a pulverization step was performed. In the pulverization step, the fired product was coarsely pulverized using a mortar until it passed through a mesh having an opening of 1 mm, and then finely pulverized using an airflow pulverizer.

  After finishing the pulverization step, heat treatment was further performed by changing the firing temperature in the range of 900 ° C to 1100 ° C. Then, it grind | pulverized and analyzed the obtained oxide powder using the X-ray-diffraction apparatus (XRD). The intensity of the main peak of the pyrochlore phase was determined from the diffraction pattern obtained as a result of the analysis. The results are shown in FIG. In FIG. 1, the main peak intensity of the pyrochlore phase is expressed as the relative intensity with respect to the peak intensity appearing near 2θ = 33 °, which is the peak of the perovskite phase, and the peak appearing near 2θ = 30 °, which is the peak of the pyrochlore phase. .

  As shown in FIG. 1, when the second heat treatment was performed at 900 ° C. to 1060 ° C., generation of a pyrochlore phase was observed. On the other hand, when the second heat treatment was performed at 1070 ° C. or higher, the main peak of the pyrochlore phase disappeared, and the generation of the pyrochlore phase was not observed.

  Next, based on the knowledge of the temperature range where the pyrochlore phase was generated, the firing conditions were changed as shown in Table 3 below to produce an oxide powder having the composition of Sample 6. Specifically, the second and subsequent firing temperatures are set to a temperature at which no pyrochlore phase is generated (1080 ° C.) or a temperature at which the pyrochlore phase is generated (1000 ° C.), and the number of firing steps is as shown in Table 3. Changed. In Table 3, for example, “1190 ° C. 4 h” indicates that the firing temperature is 1190 ° and the holding temperature is 4 hours.

  Moreover, the raw material composition and each oxide powder after preliminary firing were analyzed using an X-ray diffractometer (XRD). The diffraction patterns obtained as a result of the analysis are shown in FIGS. In FIGS. 2 and 3, black circles represent the peak of the pyrochlore phase. The intensity of the main peak of the pyrochlore phase was determined from the diffraction pattern obtained as a result of the analysis.

  Furthermore, the fluidity of the mixture of the obtained oxide powder and organic polymer material was evaluated. The fluidity was evaluated by the minimum melt viscosity of the mixture. When the temperature of the mixture composed of the dielectric ceramic powder and the thermosetting resin as the organic polymer material is raised from room temperature, the viscosity decreases in the thermosetting resin portion, but when the curing temperature of the resin is reached Turn to increase. The lowest melt viscosity is the lowest viscosity of the mixture in the process. Specifically, the minimum melt viscosity was measured after adding 40% of the oxide powder to the vinylbenzyl resin in a volume ratio. And about these samples, the dielectric property was evaluated. The evaluation results of the dielectric properties are shown in Table 3 together with the evaluation results of the powder properties of the oxide powder, the minimum melt viscosity, the main peak strength of the pyrochlore phase, and the like.

  As is apparent from Table 3, the specific surface area of the oxide powder is reduced by repeating firing and pulverization, and the fluidity of the mixture of the oxide powder and the resin is improved.

  In addition, as shown in FIG. 2, no pyrochlore phase was observed in the oxide powder after the first firing. In addition, as shown in FIG. 3, no pyrochlore phase was observed when the second and subsequent firing temperatures were set to 1080 ° C. However, when the second and subsequent firing temperatures were set to 1000 ° C., the formation of a pyrochlore phase was confirmed after the second and third firings. As shown in Table 3, when all the second and subsequent firing temperatures were set to 1000 ° C., the final firing temperature in the second and subsequent firing / pulverization steps was set to 1080 ° C., although the target dielectric properties were satisfied. Compared with the case, the dielectric properties tend to deteriorate.

  As described above, from the results of Experiment 2, when the oxide powder is produced, the fluidity of the mixture of the oxide powder and the resin is improved by repeating the firing process and the pulverization process. It turns out that manufacture becomes easy. It can also be seen that the dielectric properties of the composite dielectric material can be further improved by setting the final firing temperature in the second and subsequent firing / pulverization steps to be higher than the temperature range in which the pyrochlore phase is generated.

<Experiment 3: Fabrication of Cross Base Material Coated Prepreg and Composite Dielectric Substrate Using This>
Various dielectric ceramic powders used in Sample 6 and Sample 25 of Experiment 1 and an organic polymer material (polyvinylbenzyl ether compound) were sufficiently mixed in toluene so that the volume ratio was a predetermined ratio. This slurry was applied to a glass cloth (manufactured by Asahi Schwer) having a cloth mass of 40 g / m ² and a thickness of 50 μm with a coating machine, dried at 110 ° C., and then used as a prepreg. The thickness of this prepreg was 160 μm.

Next, 10 sheets of the prepared prepregs were stacked and pressed at 150 ° C. with a press pressure of 4.0 × 10 ⁶ Pa, followed by thermosetting at 200 ° C. to prepare a composite dielectric substrate having a thickness of 1.4 mm. . Then, a rod-shaped sample (1.4 mm × 1.4 mm × 9 mm) was cut out and used as a measurement sample.

  These samples were evaluated for relative dielectric constant εr, Q value, and temperature characteristic τε. The results are shown in Table 4.

  Even in a composite dielectric substrate manufactured using a prepreg, excellent characteristics are exhibited with respect to each characteristic of relative permittivity εr, Q value, and temperature characteristic τ.

It is a characteristic view which shows the relationship between the heat processing temperature of oxide powder, and the main peak intensity | strength of the pyrochlore phase of oxide powder. It is a X-ray-diffraction pattern of the oxide powder obtained by the pre-baking thing and the baking conditions of Table 3 upper stage. It is an X-ray-diffraction pattern of the oxide powder obtained by the temporary baking thing and the baking conditions of the lower stage of Table 3.

Claims (34)

A composite dielectric material containing a dielectric ceramic and an organic polymer material,
As the dielectric ceramic, a general formula (M, Li, Bi, RE) _x TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents La, Ce, Pr, Nd, And at least one selected from Sm, Y, Yb, and Dy, and 0.9 ≦ x ≦ 1.05). Composite dielectric material. The basic composition component of the oxide powder is aBaTiO ₃ —bSrTiO ₃ —cCaTiO ₃ —dLi _1/2 Bi _1/2 TiO ₃ —eLi _1/2 RE _1/2 TiO ₃ [where RE is La, Ce, Pr , Nd, Sm, Y, Yb, Dy are represented, and a to e represent the blending ratio (mol%) of each component. ],
0 ≦ a ≦ 5
0 ≦ b ≦ 20
10 ≦ c ≦ 45
a + b + c ≦ 50
b + d / 2 ≦ 33
c + d / 2 ≦ 65
a + b + c + d + e = 100
The composite dielectric material according to claim 1, wherein: _3. The composite dielectric material according to claim 2, wherein RE is Nd in Li _1/2 RE _1/2 TiO ₃ among the basic composition components.   4. The composite dielectric material according to claim 3, wherein a part of the Nd is substituted with at least one selected from La, Ce, Pr, Sm, Y, Yb, and Dy. 5. The composite dielectric material according to claim 1, wherein the oxide powder has a specific surface area of 9 m ² / cm ³ or less.   The composite dielectric material according to claim 1, wherein the organic polymer material is a thermoplastic resin.   6. The composite dielectric material according to claim 1, wherein the organic polymer material is a thermosetting resin.   8. The composite dielectric material according to claim 7, wherein the thermosetting resin is a vinyl benzyl resin.   9. The composite dielectric material according to claim 8, wherein the vinyl benzyl resin is mainly composed of a polyvinyl benzyl ether compound.   A prepreg obtained by applying a slurry obtained by dispersing the composite dielectric material according to any one of claims 1 to 9 in a solvent to a cloth substrate and drying the slurry.   The prepreg according to claim 10, wherein the cloth substrate is a glass cloth. The prepreg according to claim 11, wherein the glass cloth has a cloth mass of 40 g / m ² or less and a thickness of 50 μm or less.   A metal foil coated product obtained by coating a slurry obtained by dispersing the composite dielectric material according to any one of claims 1 to 9 on a metal foil and drying the slurry.   The metal foil coated product according to claim 13, wherein the metal foil is a copper foil.   10. A molded article obtained by drying and molding a slurry in which the composite dielectric material according to any one of claims 1 to 9 is dispersed in a solvent.   A composite dielectric substrate comprising the composite dielectric material according to claim 1.   The composite dielectric substrate according to claim 16, wherein the composite dielectric substrate is formed by heating and pressurizing the prepreg according to claim 10.   The composite dielectric according to claim 16, which is formed by heating and pressing the prepreg according to any one of claims 10 to 12 in a state of being sandwiched between metal foils, and has metal foils on both sides. substrate.   19. The composite dielectric substrate according to claim 18, wherein the metal foil is a copper foil.   The metal foil coated product according to claim 13 or 14 is bonded to both surfaces of the cloth substrate so that the coated surfaces are in contact with each other, and is formed by heating and pressing in this state, and has a metal foil on both surfaces. The composite dielectric substrate according to claim 16.   21. The composite dielectric substrate according to claim 20, wherein the cloth substrate is a glass cloth. The composite dielectric substrate according to claim 21, wherein the glass cloth has a cloth mass of 40 g / m ² or less and a thickness of 50 µm or less.   The composite dielectric substrate according to claim 16, wherein the composite dielectric substrate is formed by heating and pressing the molded body according to claim 15.   The composite dielectric substrate according to claim 16, wherein the composite dielectric substrate is formed by heating and pressurizing the molded body according to claim 15 while being sandwiched between the metal foils, and has metal foil on both sides.   The composite dielectric substrate according to claim 24, wherein the metal foil is a copper foil.   26. The composite dielectric substrate according to claim 16, wherein the composite dielectric substrate is used in a high frequency band of 500 MHz or more.   The prepreg according to any one of claims 10 to 12, the coated metal foil according to claim 13 or 14, the molded body according to claim 15, and the composite dielectric according to any one of claims 16 to 26. A multilayer substrate having a multilayer structure including at least one selected from substrates as a multilayer element, the multilayer element including the multilayer element.   28. The multilayer substrate according to claim 27, wherein the multilayer substrate is used in a high frequency band of 500 MHz or more. A general formula (M, Li, Bi, RE) _x through a firing step of obtaining a fired product by holding the raw material composition at a predetermined firing temperature and a grinding step of grinding the fired product using an airflow grinder. TiO ₃ (where M represents at least one selected from Ba, Sr, and Ca, and RE represents at least one selected from La, Ce, Pr, Nd, Sm, Y, Yb, and Dy. 0.9 ≦ x ≦ 1.05)), and an oxide powder having a composition represented by:
A method for producing a composite dielectric material, comprising mixing a dielectric ceramic containing the oxide powder and an organic polymer material.   30. The method for producing a composite dielectric material according to claim 29, wherein the firing step and the crushing step are repeated.   31. The method for producing a composite dielectric material according to claim 30, wherein a firing temperature in the last firing step is set higher than a temperature range in which a pyrochlore phase is generated in the oxide powder.   32. The method for producing a composite dielectric material according to claim 30, wherein the firing temperature in the second and subsequent firing steps is lower than the firing temperature in the first firing step.   The method for producing a composite dielectric material according to claim 32, wherein a difference between a firing temperature in the first firing step and a firing temperature in the second and subsequent firing steps is 50 ° C or more.   The method for producing a composite dielectric material according to claim 33, wherein a difference between a firing temperature in the first firing step and a firing temperature in the second and subsequent firing steps is 100 ° C or higher.

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