Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-08-02
2001-03-27
Sough, Hyung-Sub (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S256000, C501S032000, C501S065000, C361S792000, C029S843000, C029S830000, C029S825000, C428S209000
Reexamination Certificate
active
06207905
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a glass-ceramic composition for use, for example, in a circuit substrate or a chip component, a circuit substrate using the composition and a method of manufacturing the circuit substrate.
(ii) Description of the Related Art
Recently, in response to request for higher performance of ceramic substrates and miniaturization of chip components, a glass ceramic substrate has been turned to practical use Detail compositions, manufacture methods, and the like are described in Japanese Patent Publication Nos. 97565/1994 and 69902/1994.
For example, Japanese Patent Publication No. 97565/1994 discloses a glass ceramic composition in Example 1, in which a weight ratio of glass and Al
2
O
3
is 66:34 (33.5 wt %: 17.1 wt %). The glass is composed of 17.2 wt % of PbO, 4.5 wt % of B
2
O
3
, 56.5 wt % of SiO
2
, 9.1 wt % of Al
2
O
3
, 8.6 wt % of CaO, 2.4 wt % of Na
2
O, and 1.7 wt % of K
2
O. A glass deformation temperature is 590° C., a softening point is 660° C., and a difference of the softening point and deformation temperature is 70° C. It is further described that a glass ceramic tape obtained by sintering the glass-ceramic composition is superior in dimensional stability.
Moreover, Japanese Patent Publication No. 69902/1994 discloses a glass ceramic composition in Example 1, which is composed of 60 wt % of glass and 40 wt % of Al
2
O
3
The glass is composed of 50 wt % of SiO
2
, 6 wt % of Al
2
O
3
, 35 wt % of PbO, 5 wt % of (MgO+CaO+SrO+BaO), 1 wt % of ZnO, 0.5 wt % of B
2
O
3
, 0 wt % of (Li
2
O+Na
2
O+K
2
O), and 2.5 wt % of (TiO
2
+ZrO
2
). It is described that when the composition is formed into a slurry and a resulting green sheet is fired, an obtained substrate has large resistance strength and large thermal conductivity, and is superior in thermal resistance and chemical resistance. It is further described that when Ag—Pd conductors are formed on the green sheet by screen printing, laminated and fired to form a glass-ceramic laminate, a multilayered circuit element is superior in solder wettability and bonding strength.
These glass-ceramic compositions or the glass-ceramic composites have been heretofore used as circuit substrates by forming conductor paths inside or on the surface of the each layer or the laminate. However, matching properties with various conductor materials have not been studied sufficiently.
The present inventors have studied this respect, and found out the following problems. Specifically, in the case where a glass composition having a high softening point is employed, when an Ag or Au system conductor circuit is screen-printed on the green sheet and then fired, conductor materials are dispersed in a ceramic, thereby deteriorating an insulating resistance, dielectric constant and other electric properties of the ceramic. A performance could not be obtained as designed. Moreover, in the case where a glass composition having a low softening point is employed, since the Ag or Au system conductor material is not sufficiently sintered, a bonding strength of the glass-ceramic composite and conductor circuit probably becomes insufficient. One of problems is the warp, or deformation of the substrate when the substrate is fired together with the conductive materials. For example, in a substrate in which a large number of pieces each of about 1×10 mm are arranged on a large plate with a size of about 100×100 mm, the generation of the warp, or deformation causes a fatal defect in a solder printing process after the substrate is fired, or in a process for mounting electronic components or parts.
SUMMARY OF THE INVENTION
Wherefore, an object of the present invention is to provide a glass-ceramic composition excellent in various properties of a ceramic and also excellent in matching properties with an Ag or Au system conductor material, a circuit substrate using the composition and a method of manufacturing the circuit substrate.
To attain this and other objects, according to a first aspect of the present invention, there is provided a glass-ceramic composition in which a weight ratio of a glass and a ceramic is 40 to 60:60 to 40. The glass is composed of 40 to 60 wt % of SiO
2
, 5 to 9 wt % of Al
2
O, 1 to 10 wt % of B
2
O, 3 to 5 wt % of Na
2
O+K
2
O, 3 to 15 wt % of CaO+MgO+ZnO, and 15 to 40 wt % of PbO, and does not contain Li
2
O. A softening point of the glass is in the range of 650 to 780°.
As physical properties of the glass in the glass-ceramic composition, it is preferred that a difference of the softening point and a yield point be 95° C. or higher and that a glass transition point be in the range of 520 to 620° C. The glass-ceramic composition is preferably fired at a firing temperature of 800 to 930° C. under an oxidizing atmosphere. As the ceramic, alumina, silica, mullite, magnesia, titania, zirconia, spinel, forsterite, strontium titanate, calcium titanate and the like are preferably used alone or appropriately mixed for use.
According to a second aspect of the present invention, there is provided a circuit substrate which includes a layered substrate formed by laminating a plurality of insulating substrates, and a conductor circuit formed at least on a surface of each of the plurality of the insulating substrates.
The insulating substrate is formed of the glass-ceramic composition according to the first aspect of the present invention.
The conductor circuit is preferably formed of an Ag or Au system conductor, and has an inductance circuit or a capacitance circuit.
According to a third aspect of the present invention, there is provided a method of manufacturing a circuit substrate which is provided with a step of preparing a green sheet composed of the glass-ceramic composition of the first aspect, a step of forming an Ag or Au system conductor layer at least on a surface of the green sheet, a step of laminating a plurality of green sheets each having the conductor layer formed thereon, and a step of firing the laminated green sheets at a firing temperature in the range of 800 to 930° C. under an oxidizing atmosphere.
In a conventional circuit substrate using a Cu conductor as a low resistance concuctor, a heat-resistant epoxy resin is used as a substrate material. Since the heat-resistant epoxy resin has a large dielectric loss in a microwave band, a signal transmission loss is also large. This causes a problem that such resin is not suitable for an application to the substrate used in the microwave band. Therefore, for the microwave band, both the conductor loss and the dielectric loss need to be small. In this respect, the circuit substrate of the present invention using the Ag or Au system conductor material is superior.
In the glass-ceramic composition of the present invention, the glass and ceramic weight ratio is 40 to 60:60 to 40 for the following reasons:
Specifically, when a glass content is less than 40 relative to the entire glass and ceramic weight of 100, the amount of glass components for covering peripheries of ceramic particles becomes insufficient during the firing of the glass-ceramic composition to form the insulating substrate. An excellent wetting cannot be obtained, an apparent porosity of the substrate fails to become zero, and a substrate strength is lowered. On the other hand, when the glass content exceeds 60, a sufficient bending strength cannot be obtained. Additionally, the glass-ceramic composition may be constituted only of the glass and the ceramic, or may contain other components. Moreover, in a preferable range, the glass and ceramic weight ratio is 45 to 55:55 to 45.
A glass component SiO
2
is a glass network former and a glass basic composition. The content of SiO
2
is in the range of 40 to 60 wt %, because when the content is less than 40 wt %, the softening point tends to be lower than 650° C. When the content exceeds 60 wt %, the softening point tends to become hi-her than 780° C., and a sufficient strength cannot be obtained.
Another glass component Al
2
O
3
enhanc
Taga Shigeru
Takahashi Hiroyuki
Yoshida Yoshitaka
NGK Spark Plug Co. Ltd.
Patel Ishwar B.
Sough Hyung-Sub
Sughrue Mion Zinn Macpeak & Seas, PLLC
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