Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-02-20
2002-06-11
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C501S010000, C501S011000
Reexamination Certificate
active
06403199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an insulating ceramic for use in, for example, multilayer circuit boards. Specifically, the present invention relates to a high-frequency insulating ceramic which is advantageously used in, for example, composite multilayer circuit boards equipped with semiconductor devices and various electronic parts and which can be obtained by firing in conjunction with conductive materials such as copper and silver, as well as to a multilayer ceramic substrate, a ceramic electronic part, and a laminated ceramic electronic part each using the insulating ceramic.
2. Description of the Related Art
Recent tendencies to accelerate the use of electronic equipment in higher frequencies keep on expanding. With such demands for the accelerating, higher-density mounting and higher-density packing of electronic parts which are used in such electronic equipment are still increasing. To satisfy these demands, multilayer circuit boards are conventionally used as substrates on which semiconductor devices and various electronic parts are mounted. In such a multilayer circuit board, the substrate houses a conductor circuit and an electronic part functional device to thereby further miniaturize electronic equipment.
Alumina has been conventionally frequently used as a material for constituting the multilayer circuit board.
Alumina has a relatively high firing temperature of 1500° C. to 1600° C., and refractory metals such as Mo, Mo—Mn, and W must be generally used as materials for conductive circuits housed in such a multilayer circuit board composed of alumina.
However, these refractory metals have a high electric resistance. Strong demands have been therefore made for the use of a metal such as copper as a conductive material, which metal has a lower electric resistance and is available at a lower cost than the refractory metals. To use copper as a conductive material, the use of a glass ceramic or crystallized glass which can be obtained by firing at low temperatures of 1000° C. or less has been proposed (e.g., Japanese Unexamined Patent Application Publication No. 5-238774).
However, such known substrate materials which can be obtained by firing at low temperatures have a low mechanical strength and a low Q-value, and the firing process tends to affect the type and proportion of deposited crystal phases of such materials.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an insulating ceramic which can solve the problems of the conventional technologies, can be obtained by firing at low temperatures, can be obtained by firing in conjunction with conductive materials having relatively low melting points such as silver and copper, has satisfactory mechanical strength and a high Q-value, and is insensitive to the type and proportion of deposited crystal phases.
Another object of the present invention is to provide a multilayer ceramic substrate, a ceramic electronic part and a laminated ceramic electronic part, each of which is composed of the insulating ceramic, which has satisfactory mechanical strength and a high Q-value, and is insensitive to the type and proportion of deposited crystal phases.
After intensive investigations to solve the above problems, the present inventors found that the deposition of MgAl
2
O
4
crystal phase and Mg
3
B
2
O
6
crystal phase and/or Mg
2
B
2
O
5
crystal phase as major crystal phases can yield a higher Q-value and a higher reliability. This is because the deposition of Mg
3
B
2
O
6
crystal phase and/or Mg
2
B
2
O
5
crystal phase as major crystal phases in addition to MgAl
2
O
4
crystal phase stabilizes boron in the glass to thereby improve reliability and sinterability. The present invention has been accomplished based on these findings.
Specifically, the present invention provides, in a broad aspect, an insulating ceramic including a fired mixture of a MgO—MgAl
2
O
4
ceramic and a borosilicate glass, in which MgAl
2
O
4
crystal phase and at least one of Mg
3
B
2
O
6
crystal phase and Mg
2
B
2
O
5
crystal phase are deposited as major crystal phases. In this context, “major” means that of the phases present, the MgAl
2
O
4
crystal phase and the Mg
3
B
2
O
6
and/or Mg
2
B
2
O
5
crystal phase are present in the greatest amounts.
The borosilicate glass for use in the present invention preferably includes boron oxide, silicon oxide, magnesium oxide and an alkali metal oxide. The combination use of MgO—MgAl
2
O
4
with a glass composition including at least boron oxide (B
2
O
3
), silicon oxide (SiO
2
), magnesium oxide (MgO) and an alkali metal oxide (e.g., Na
2
O, K
2
O or Li
2
O) allows the MgAl
2
O
4
crystal phase and Mg
3
B
2
O
6
crystal phase and/or Mg
2
B
2
O
5
crystal phase to deposit as major crystal phases to thereby yield a high Q-value.
In this case, the borosilicate glass preferably includes about 15 to 65% by weight of boron oxide in terms of B
2
O
3
, about 8 to 50% by weight of silicon oxide in terms of SiO
2
, about 10 to 45% by weight of magnesium oxide in terms of MgO and 0 to about 20% by weight of an alkali metal oxide in terms of R
2
O, wherein R is an alkali metal.
If the content of boron oxide in borosilicate glass is less than about 15% by weight in terms of B
2
O
3
, the ratio of boron oxide to MgO in the system is low, resulting in decreased deposition of the Mg
3
B
2
O
6
crystal phase and/or Mg
2
B
2
O
5
crystal phase. A high reliability and a satisfactory sinterability may not be obtained.
On the contrary, if the content of boron oxide is more than about 65% by weight, the moisture resistance of the glass may be deteriorated.
If the content of silicon oxide in the glass is less than about 8% by weight in terms of SiO
2
, the chemical stability of the glass may be deteriorated, and if it exceeds about 50% by weight, the resulting glass may have an increased fusing temperature or a deteriorated sinterability.
A magnesium oxide content in the glass of less than about 10% by weight in terms of MgO may retard crystallization, and a content of more than about 45% by weight may cause crystallization in the manufacture of the glass to thereby deteriorate sinterability.
The alkali metal oxide in the glass acts to decrease the fusing temperature of the glass. However, a content of the alkali metal oxide exceeding about 20% by weight may decrease Q-value.
The Mg
3
B
2
O
6
or Mg
2
B
2
O
5
crystal phase can be selectively deposited by appropriately adjusting the ratio of magnesium oxide to boron oxide in the system in the present invention. Specifically, the Mg
3
B
2
O
6
crystal phase can be deposited when magnesium oxide (MgO) is excess such that the molar ratio of MgO to B
2
O
3
is more than about 3:1.
To the contrary, the Mg
2
B
2
O
5
crystal phase can be deposited when B
2
O
3
is excess such that the molar ratio of MgO to B
2
O
3
is less than about 3:1.
When the molar ratio of MgO to B
2
O
3
is in the vicinity of 3:1, both the Mg
3
B
2
O
6
and Mg
2
B
2
O
5
crystal phases are deposited.
The borosilicate glass preferably further includes 0 to about 20% by weight of aluminium oxide. The addition of aluminium oxide enhances chemical stability of the glass. However, if the content of aluminium oxide exceeds about 20% by weight, a sufficient sinterability may not be obtained.
Preferably, the borosilicate glass further includes about 30% by weight or less of zinc oxide. The addition of zinc oxide (ZnO) in the above proportion decreases the fusing temperature of the glass, and the insulating ceramic can be obtained by firing at lower temperatures. A content of zinc oxide exceeding about 30% by weight may deteriorate the chemical stability of the glass.
Preferably, the borosilicate glass further includes 0 to about 10% by weight of copper oxide. The addition of copper oxide (CuO) yields the insulating ceramic by firing at lower temperatures. A content of copper oxide exceeding about 10% by weight may result in a decreased Q-value.
The weight ratio of the MgO—MgAl
2
O
4
ceramic to the borosilicate glass is prefe
Chikagawa Osamu
Mori Naoya
Blackwell-Rudasill Gwendolyn
Dickstein , Shapiro, Morin & Oshinsky, LLP
Jones Deborah
Murata Manufacturing Co. Ltd
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