Use of zeolites in preparing low temperature ceramics

Details Use of zeolites in preparing low temperature ceramics Use of zeolites in preparing low temperature ceramics

2002-08-16

2004-05-18

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

Reexamination Certificate

active

06737374

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a dielectric ceramic article precursor and a process for preparing a dielectric ceramic article. The precursor article comprises a crystalline zeolite or an amorphous aluminosilicate in combination with a glass phase.
BACKGROUND OF THE INVENTION
The demand for smaller and multifunction electronic devices such as wireless phones with internet access, PDA, etc. has necessitated an ever increasing density of multilayer circuits. These multilayer circuits typically use dielectric materials which act as insulating substrates onto which are deposited conducting metals to form a wiring layer.
Very early on, alumina was the dielectric material of choice, which because of its high sintering temperature (1400°-1500° C.) necessitated the use of metals such as tungsten or molybdenum. However, as signal transmission speeds have increased to 1 GHz and above, the use of tungsten or molybdenum wire is not possible because of their high resistivity. This necessitates the use of lower resistivity metals such as gold, silver or copper. These metals, however, have much lower melting temperatures which in turn require dielectrics which sinter at temperature as low as 900° C.
The art has attempted to meet this need with low temperature cofired ceramics (LTCC). These ceramics are formed by mixing, glassy materials with crystalline phases. For example, U.S. Pat. No. 5,821,181 discloses forming a mixture of alumina, a glassy precursor material and a modifier. The glassy material contains SiO
2
, B
2
O
3
, at least one of MgO, CaO, SrO and BaO and at least one of K
2
O, Na
2
O and Li
2
O; while the modifier is selected from TiO
2
, SrTiO
3
and CaTiO
3
. U.S. Pat. No. 4,714,687 discloses preparing a glass-ceramic containing willemite as the crystalline phase. The glass-ceramic body contains ZnO, MgO, Al
2
O
3
and SiO
2
. U.S. Pat. No. 5,164,342 discloses a low dielectric glass ceramic containing CaO, B
2
O
3
and SiO
2
. In U.S. Pat. No. 6,232,251 B1 a dielectric ceramic is disclosed which comprises a diopside oxide crystal phase; a crystal phase selected from a quartz crystal phase and a composite oxide crystal phase containing Ti and Mg or Zn and a glass phase.
It is also disclosed in the art that zeolitic compositions can be sintered directly into ceramics. Thus, U.S. Pat. No. 5,071,801 discloses preparing a high density leucite based ceramic from a potassium, cesium or rubidium exchanged zeolite. The zeolite has a SiO
2
/Al
2
O
3
ratio of 3.5 to about 7.5. Similarly U.S. Pat. Nos. 4,980,323 and 5,064,790 disclose a process and a cordierite ceramic prepared by the process. The cordierite can be prepared from a Mg exchanged zeolite such as zeolite B, philipsite, harmotone, gismondine, zeolite ZK-19 and zeolite W. Further, U.S. Pat. No. 5,036,030 discloses a process for preparing an alkaline earth metal aluminosilicate sintered body from a mixture of a zeolite in the alkaline earth metal form, having a SiO
2
/Al
2
O
3
ratio of not more than 3.0 and a boron compound such as boron oxide. Finally, U.S. Pat. No. 5,166,107 discloses preparing an anorthite sintered body from a calcium type zeolite having a SiO
2
/Al
2
O
3
ratio of less that 3.0.
In contrast to this art, applicant has prepared a dielectric ceramic article from a mixture of a crystalline aluminosilicate zeolite and a glass phase. The mixture can also contain a metal oxide additive such as B
2
O
3
or SrTiO
3
. The advantage to the use of zeolites in forming dielectric ceramic articles is that the higher reactivity of zeolite-derived powders vs. crystalline ceramic fillers such as alumina and cordierite allows more facile and complete solid state reaction during sintering and therefore easier formation of desired high-Q phases. Other advantages include increased uniformity in the resulting composition and associated increased uniformity in its electrical properties.
SUMMARY OF THE INVENTION
One embodiment of the present invention is a ceramic article precursor comprising from about 1% to about 99% by weight of a crystalline aluminosilicate zeolite or an amorphous aluminosilicate derived from the zeolite and from about 99% to about 1% by weight of a glass phase, the crystalline aluminosilicate zeolite having a composition on an anhydrous basis represented by an empirical formula of:
A
1

Si
x
AlO
y
where A is an exchangeable cation selected from the group consisting of alkali metals, alkaline earth metals, transition metals, zinc, rare earth metals and mixtures thereof, “n” is the valence of A and has a value from about 1 to about 3, “x” has a value from about 1 to about 10 and “y” has a value which balances the sum of the valences of (A+Si+Al).
A process for preparing a dielectric ceramic article comprising forming a mixture of a crystalline aluminosilicate zeolite or an amorphous aluminosilicate derived from the zeolite and a glass phase into a shaped article and calcining the shaped article at a temperature of about 700° to about 1000° C. for a time of about 0.5 to about 24 hrs, the crystalline aluminosilicate zeolite having a composition on an anhydrous basis represented by an empirical formula of:
A
1

Si
x
AlO
y
where A is an exchangeable cation selected from the group consisting of alkali metals, alkaline earth metals, transition metals, zinc, rare earth metals and mixtures thereof, “n” is the valence of A and varies from about 1 to about 3, “x” has value from about 1 to about 10 and “y” has a value which balances the sum of the valences of (A+Si+Al) and where the zeolite or amorphous aluminosilicate is present in an amount from about 1 wt. % to about 99 wt. % and the glass phase is present in an amount from about 99 wt. % to about 1 wt. %.
These and other objects and embodiments will become more apparent after a detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As stated, the present invention relates to a ceramic article precursor and a process for preparing a dielectric ceramic article. One essential element of the invention is a crystalline aluminosilicate zeolite or an amorphous aluminosilicate derived from the zeolite. Zeolites are well known microporous three-dimensional framework structures. In general, the crystalline zeolites are formed from corner sharing AlO
2
and SiO
2
tetrahedra and are characterized as having pore openings of uniform dimensions, having a significant ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal pores or voids of the crystal without displacing any atoms which make up the permanent crystal structure. Zeolites can be represented on an anhydrous basis, by the formula:
A
1

Si
x
AlO
y
where A is a cation having the valence of “n”, “x” has a value of about 1 to about 10. In naturally occurring zeolites, A can be Li, Na, Ca, K, Mg and Ba. The A cations are loosely bound to the structure and frequently can be completely or partially replaced with other cations by conventional ion exchange techniques. Therefore, A is selected from the group consisting of alkali metals, alkaline earth metals, transition metals, rare earth metals, zinc and mixtures thereof and consequently “n” has a value from about 1 to about 3. Finally, “y” has a value which balances the sum of the valences of (A+Si+Al).
The zeolites which can be used in this invention include but are not limited to phillipsite, harmotone, gismondine, zeolite B, zeolite ZK-19, zeolite W, zeolite Y, zeolite L, zeolite LZ-210, zeolite omega, zeolite LZ-202 and mixtures thereof. For a detailed explanation of the structural similarities among the phillipsite group of zeolites, i.e. phillipsite, harmotome, zeolite B, zeolite ZK-19 and zeolite W and a list of references where specific structural information about these zeolites may be found, the reader is referred to U.S. Pat. No. 4,344,851 which is incorporated by reference. The important feature of this family of zeolites is the absence of framework sites which can be either irreversibly occupied by cations such as sodium or po

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