Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Of electrical article or electrical component
Reexamination Certificate
1999-11-30
2001-08-07
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Of electrical article or electrical component
C264S619000, C264S642000
Reexamination Certificate
active
06270716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of low-temperature firing ceramic compositions which are used as, for example, dielectric ceramics for microwave resonators, high-frequency filters and monolithic capacitors, and ceramics for multilayered substrates.
2. Description of the Related Art
To miniaturize electronic parts such as microwave resonators and high-frequency filters, efforts have been made to replace cavity resonators with dielectric ceramics each having a high dielectric constant. Such a dielectric resonator utilizes the effect that the wavelength of an electromagnetic wave is shortened inside a dielectric to 1/&egr;
½
the wavelength in free space, wherein &egr; is the dielectric constant of the dielectric.
However, a dielectric ceramic having such a temperature coefficient such as to be applicable as a dielectric resonator can only have a specific dielectric constant &egr;r of at most 100, which is insufficient to meet the requirements of further miniaturization of resonators in recent years.
An effective solution to this requirement under the limitation of low specific dielectric constant &egr;r of dielectric ceramics is to use LC resonators which are employed in microwave circuits. In addition, the application of a lamination forming process, which has practically been applied to monolithic capacitors and multilayer substrates, to the construction of LC resonant circuits can give further miniaturized electronic parts having high reliability.
To obtain LC resonators each having a high Q-value in a microwave band by the lamination forming process, the internal electrodes to be integrated in monolithic capacitors or multilayer substrates must have a high electrical conductivity. In other words, such internal electrodes must be composed of gold, silver, copper or another metallic material having a high electrical conductivity, which internal electrodes are cofired with dielectric ceramics or ceramics for multilayer substrates.
Thus, the dielectric materials need to be high in dielectric constant, Q-value and theimostability and to be low-temperature firing ceramic compositions which can be cofired with internal electrodes composed of a metallic material having a low melting point. Few dielectric materials, however, provide these requirements in good balance.
As a possible solution to this problem, for example, Japanese Unexamined Patent Publication No. 6-40767 discloses a technique including the steps of: (1) calcining a porcelain composition mainly containing a BaO—TiO
2
—ReO
{fraction (3/2)}
, wherein Re is a rare earth element, at a temperature of 1050° C. or higher, milling the calcined composition to a mean particle diameter of 0.8 &mgr;m or less, and adding a glass powder mainly containing B
2
O
3
to give a material powder; or (2) adding a glass powder predominantly comprising B
2
O
3
to a porcelain composition containing a BaO—TiO
2
—ReO
{fraction (3/2)}
as a main component, calcining the resultant mixture at a temperature of 1050° C. or higher, and milling the calcined mixture to a mean particle diameter of 0.8 &mgr;m or less to give a material powder; and forming and firing the material powder to give a low-temperature firing ceramic composition.
According to this technique, a dielectric porcelain composition which can be sintered at a temperature equal to or lower than the melting point of silver and has a comparatively high specific dielectric constant, a high Q-value and a low temperature coefficient of a resonant frequency is realized. However, the technique, in which a main crystalline phase (e.g., Ba(Nd,Bi)
2
Ti
4
O
12
) is not precipitated in the calcination at a low temperature of about 1000° C., requires the calcination at a high temperature of 1050° C. or higher (preferably 1100° C. to 1300° C.), and the calcination at such a high temperature entails high costs.
SUMMARY OF THE INVENTION
According to the present invention, a process for the production of low-temperature firing ceramic compositions is provided, which process can yield, with facility, low-temperature firing ceramic compositions which are sinterable at low temperatures, have a high specific dielectric constant and Q-value and satisfactory thermostability.
To be more specific, the invention provides a process for the production of low-temperature firing ceramic compositions, the process including:
a first step of admixing CuO with a BaO—TiO
2
—ReO
{fraction (3/2)}
—Bi
2
O
3
main material, wherein Re is a lanthanoid element, to give a ceramic material mixture; a second step of calcining the ceramic material mixture; a third step of milling the calcined ceramic material mixture; a fourth step of admixing a B
2
O
3
—SiO
2
glass component with the milled ceramic material mixture to give a glass-ceramic material mixture; and a fifth step of forming the glass-ceramic material mixture into a target (desired) shape and firing the formed glass-ceramic material mixture.
In the first step of the inventive process, the CuO is added in a proportion of about 0.1% to 2.0% by weight relative to 100% by weight of the main material.
The calcination in the second step is preferably be conducted at a temperature equal to or higher than 950° C.
In the third step, the calcined ceramic material mixture is preferably milled to a mean particle diameter of about 2.0 &mgr;m or less.
In the fourth step, another portion of CuO is preferably further admixed with the milled ceramic material mixture.
In the inventive process, about 80.0% to 98.0% by weight of the milled ceramic material mixture, about 1.0% to 20.0% by weight of an RO—B
2
O
3
—SiO
2
glass material as the glass component, wherein R is an alkaline earth metal element, and about 2.0% by weight or less of CuO may be admixed in the fourth step to make the glass-ceramic material mixture (100% by weight).
According to the inventive process for the production of low-temperature firing ceramic compositions, where CuO is admixed before calcination, a main crystalline phase of, for example, Ba(Nd,Bi)
2
Ti
4
O
12
is precipitated even at low calcination temperatures, and therefore a dielectric porcelain composition which can be sintered at low temperatures and has a high specific dielectric constant and a high Q-value and a satisfactory thermostability can be produced with facility.
This is because when CuO is added to a main material predominantly containing, for example, BaCO
3
, TiO
2
, ReO
{fraction (3/2)}
and Bi
2
O
3
and the resultant mixture is calcined, CuO forms a liquid phase and promotes the reaction of the main material and thereby promotes the formation of a main crystalline phase of, for instance, Ba(Nd,Bi)
2
Ti
4
O
12
. In addition, CuO anchors to the surface of the main crystalline phase particle after the calcination to thereby increase the sinterability of the main crystalline phase particle. In addition, the milling of the main crystalline phase particle increases its specific surface area to further improve the sinterability.
In particular, the addition of sintering aids including B
2
O
3
—SiO
2
or another glass component, and CuO to the milled material mixture can reduce the firing temperature to 1000° C. or below, and the resultant composition can be sintered at a temperature lower than the melting point of a conductive substance mainly containing, for example, silver, gold or copper having a low specific resistance. The increased sinterability of the main crystalline phase can minimize the proportion of the sintering aid to give low-temperature firing ceramic compositions having a high specific dielectric constant and a low dielectric loss.
Such low-temperature firing ceramic compositions can be cofired with internal electrodes composed of, for instance, gold, silver or copper having a low specific resistance, and can provide ceramic parts or multilayer ceramic substrates internally having these internal electrodes and having satisfactory high-frequency characteristics. Furthermore, the use of these dielectric porcelain compositions can give by the
Fiorilla Christopher A.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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