Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-08-30
2002-09-03
Fiorilla, Christopher A. (Department: 1731)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C264S619000
Reexamination Certificate
active
06444066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for manufacturing ceramic electronic devices, such as dielectric resonators, LC filters, laminated capacitors, and ceramic substrates.
2. Description of the Related Art
In order to miniaturize dielectric resonators and the like used in the microwave range, efforts have been made to form resonator bodies using dielectric ceramic compositions having high dielectric constants. This is to exploit a phenomenon in which, when the dielectric constant of a dielectric ceramic composition is represented by ∈·r, the wavelengths of electromagnetic waves in free space are shortened in the dielectric ceramic composition to 1/{square root over ( )}∈.
However, dielectric ceramic resonators having a temperature stability, in particular, having a temperature coefficient of static capacitance, which is practically usable, have ∈·r of at most 100, and hence, requirements for further miniaturization cannot be satisfactorily fulfilled.
Under the conditions restricted by a relative dielectric constant of ∈·r, it is effective to use LC resonator circuits, which are known as circuits for microwaves in order to achieve miniaturization of dielectric resonators. That is, when a multi-layer structure, which is practically used in laminated capacitors, ceramic multi-layer substrates and the like, is applied to LC resonator circuits, a dielectric resonator which is further miniaturized and has high reliability can be constructed.
In order to construct an LC resonator having a high Q value in the microwave range, the electrical conductivity of a conductive pattern composing the LC resonator circuit must be high. The conductive pattern simultaneously baked with a dielectric ceramic composition must be of a metal material having high conductivity, such as gold, silver or copper.
Accordingly, the dielectric ceramic composition is required to be simultaneously sinterable with the conductive pattern composed of a metal having a low melting point, such as gold, silver or copper, in addition to having a high dielectric constant, a high Q value and a small change in capacitance with temperature. Among these metals, silver is known as a noticeably effective conductive material in terms of having the highest conductivity, being relatively inexpensive and being sinterable in the air.
Concerning dielectric layers (dielectric ceramic composition) having a high dielectric constant, various compositions have been investigated, and a dielectric composition composed of BaO—TiO
2
—ReO
3/2
among those mentioned above has been known as a material having a high relative dielectric constants, a high Q value and a small temperature coefficient of static capacitance. However, the dielectric ceramic composition composed of BaO—TiO
2
—ReO
3/2
generally has a high baking temperature of at least 1,250° C., and hence, the ceramic composition cannot be simultaneously baked with a metal having a low melting point, such as gold, silver or copper. Consequently, a low temperature sintering technique has been researched in order to decrease the baking temperature to 1,000° C. or less by adding a glass component, such as borosilicate glass, lead oxide glass or the like, to the dielectric ceramic composition.
For example, in Japanese Unexamined Patent Application Publication No. 6-40767, a sintered glass ceramic compact is described which is obtained by a step of forming a glass ceramic compact having a predetermined shape from a powdered glass ceramic mixture and a step of baking the glass ceramic compact at 1,000° C. for 2 hours. The powdered glass ceramic mixture mentioned above can be prepared by steps comprising baking dielectric ceramic powder primarily composed of BaO—TiO
2
—ReO
3/2
at 1,050° C. or more, pulverizing the baked powdered glass ceramic mixture into a powder having an average particle diameter of not more than 0.8 &mgr;m, and adding glass powder primarily composed of B
2
O
3
thereto; alternatively, it can be prepared by steps comprising adding glass powder primarily composed of B
2
O
3
to dielectric ceramic powder primarily composed of BaO—TiO
2
—ReO
3/2
, baking the powdered mixture thus formed at 1,050° C. or more, and pulverizing the baked powdered mixture into a powder having an average particle diameter of not more than 0.8 &mgr;m.
According to the methods described above, a sintered glass ceramic compact which has a high relative dielectric constant, a high Q value and a small temperature coefficient of static capacitance, can be obtained by sintering at a temperature of not more than the melting point of a conductive material such as gold, silver or copper. However, since the baking time is long, such as 2 hours, when a glass ceramic compact has, in particular, a silver-based conductive pattern, substantial diffusion of silver occurs during baking, and reliability of the resulting sintered glass ceramic compact may be degraded in some cases.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a method for manufacturing a highly reliable ceramic electronic device in which diffusion of silver is suppressed when a ceramic electronic device is manufactured to provide a silver-based conductive pattern formed on a sintered glass ceramic compact primarily composed of BaO—TiO
2
—ReO
3/2
dielectric ceramic powder.
One preferred embodiment of the present invention provides a method for manufacturing a ceramic electronic device comprising the steps of blending BaO—TiO
2
—ReO
3/2
dielectric ceramic powder and glass powder to form a powdered glass ceramic mixture, in which Re is a earth rare element, molding the powdered glass ceramic mixture to form a glass ceramic compact having a predetermined shape, forming a silver-based conductive pattern on the glass ceramic compact, and heating the glass ceramic compact provided with the silver-based pattern at a heating rate of at least about 10° C./minute from a temperature of at least 500° C. and holding the glass ceramic compact above 500° C. for about 20 to 90 minutes.
In the above described method, the heating step may comprise heating the glass ceramic compact to the maximum temperature being used at the heating rate in the temperature range mentioned above, i.e., above about 500° C., holding the glass ceramic compact at the maximum temperature for about 10 to 60 minutes, and cooling the glass ceramic compact at a cooling rate of at least about 10° C./minute in the temperature range.
In the above described method, the dielectric ceramic powder may have a composition represented by the formula xBaO—yTiO
2
—zReO
3/2
, in which 5≦x≦20, 52.5≦y≦70, 15≦z≦42.5, and x+y+z=100.
In the above described method, the dielectric ceramic powder may comprise about 3 to 30 percent by weight of bismuth oxide calculated of as Bi
2
O
3
.
In the above described method, the glass powder may be borosilicate glass powder comprising SiO
2
and B
2
O
3
.
In the above described method, the glass powder may comprise about 13 to 50 percent by weight of SiO
2
, about 3 to 30 percent by weight of B
2
O
3
, about 40 to 80 percent by weight of an alkaline earth metal oxide and about 0.1 to 10 percent by weight of an alkali metal oxide.
In the above described method, the powdered glass ceramic mixture may comprise copper oxide powder.
In the above described method, the powdered glass ceramic mixture may comprise about 75 to 95 percent by weight of the dielectric ceramic powder, about 2 to 20 percent by weight of the glass powder and not more than about 5 percent by weight of the copper oxide powder.
According to the method for manufacturing the ceramic electronic device of the present invention, since the glass ceramic compact provided with the silver-based conductive pattern is heated (baking treatment) at a heating rate of at least about 10° C./minute in the temperature range of at least 500° C. and is held in the temperature range for about 20 to 90 minutes, diffusion of silver can be suppre
Dickstein , Shapiro, Morin & Oshinsky, LLP
Fiorilla Christopher A.
Murata Manufacturing Co. Ltd.
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