Insulative ceramic compact

Details Insulative ceramic compact Insulative ceramic compact

2001-07-19

2004-03-30

Cuneo, Kamand (Department: 2827)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S053000, C501S073000, C501S077000, C501S108000, C501S123000, C428S210000, C174S258000

Reexamination Certificate

active

06713417

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an insulative ceramic compact for use in, for example, a multilayer circuit board. Specifically, the present invention relates to an insulative ceramic compact that can be advantageously used in a composite multilayer circuit board on which a semiconductor device or a variety of electronic parts is mounted, and can be obtained by firing in conjunction with a conductive material such as copper or silver.
2. Description of the Related Art
Recent tendencies to accelerate and to use electronic equipment in higher frequencies keep on expanding. With such tendencies, demands for the accelerating, higher-density mounting and higher-density packing of electronic parts which are used in such electronic equipment are 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 conductive 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 from 1500° C. to 1600° C., and high-melting (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 on 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).
Alternatively, the use of a ceramic having a thermal expansion coefficient close to that of Si as a material for such multilayer circuit boards has been proposed, in consideration of connection with semiconductor devices such as Si chips (Japanese Unexamined Patent Application Publication No. 8-34668).
However, these conventional substrate materials that can be fired at low temperatures have low mechanical strengths and a low Q value, and the type and proportion of the deposited crystal phase are readily affected by the firing process.
Additionally, the substrate materials described in Japanese Unexamined Patent Application Publications No. 5-238774 and No. 8-34668 cannot be significantly sintered in conjunction with highly dielectric materials having a high thermal expansion coefficient.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an insulative ceramic compact that can solve the above problems, can be obtained by firing at low temperatures and can be obtained by firing in conjunction with a conductive material having a relatively low melting point such as silver or copper, has a low relative dielectric constant, and has satisfactory high-frequency characteristics and a high thermal expansion coefficient.
Another object of the present invention is to provide a multilayer ceramic substrate which is composed of the aforementioned insulative ceramic compact, can be obtained by firing at low temperatures, has a low relative dielectric constant and satisfactory high-frequency characteristics, and can be obtained by sintering in conjunction with a highly dielectric material having a high thermal expansion coefficient, as well as to provide a ceramic electronic part using the multilayer ceramic substrate.
Specifically, the present invention provides, in an aspect, an insulative ceramic compact which includes a fired mixture of (A) a MgAl
2
O
4
ceramic powder; and (B) a glass powder including from about 13 to 50% by weight of silicon oxide calculated as SiO
2
, from about 8 to 60% by weight of boron oxide calculated as B
2
O
3
, from 0 to about 20% by weight of aluminum oxide calculated as Al
2
O
3
, and from about 10 to 55% by weight of magnesium oxide calculated as MgO.
The content of silicon oxide in terms of SiO
2
in the glass powder is from about 13 to 50% by weight, and preferably from about 20 to 30% by weight relative to the total weight of the glass powder. If the content of silicon oxide is less than about 13% by weight, the resulting sintered compact has a decreased degree of crystallization and a decreased Q value. In contrast, if it exceeds about 50% by weight, the resulting glass has an excessively high melting temperature.
The content of boron oxide in terms of B
2
O
3
in the glass powder is from about 8 to 60% by weight and preferably from about 30 to 60% by weight, relative to the total weight of the glass powder. The boron oxide mainly acts as a fusing agent (flux). If the content of boron oxide in terms of B
2
O
3
is less than about 8% by weight, the melting temperature becomes excessively high, and if it exceeds 60% by weight, the resulting sintered compact has a decreased moisture resistance.
In the glass powder, the content of aluminum oxide in terms of Al
2
O
3
is from 0 to about 20% by weight relative to the total weight of the glass powder. The aluminum oxide content in terms of Al
2
O
3
may be 0% by weight, that is, aluminum oxide may not be necessarily contained in the glass powder. Accordingly, when the insulative ceramic compact according to the present invention contains no aluminum oxide, it is an insulative ceramic compact composed of a fired mixture of (A) MgO—MgAl
2
O
4
ceramic powder and (B) a glass powder including from about 13 to 50% by weight of silicon oxide in terms of SiO
2
and from about 3 to 60% by weight of boron oxide in terms of B
2
O
3
.
When the content of aluminum oxide in terms of Al
2
O
3
in the glass powder exceeds about 20% by weight, the resulting sintered compact cannot become sufficiently dense and has a decreased Q value. The lower limit of the aluminum oxide content in terms of Al
2
O
3
, if it is contained, is any value more than 0% by weight.
The glass powder preferably contains from about 10 to 55% by weight of MgO. MgO plays a role to decrease a melting temperature in the manufacture of glass and also plays a role as a component constituting crystals in a crystallized glass. Particularly, a MgO—B
2
O
3
compound exhibits a Qf value of several ten thousands gigahertz or more and is a predominant factor to exhibit satisfactory high-frequency characteristics. If the content of MgO is less than about 10% by weight, the resulting insulative ceramic compact has a decreased Q value, and if it exceeds about 55% by weight, the insulative ceramic compact may have excess amounts of deposited crystals to thereby deteriorate the strengths of the substrate.
The glass powder for use in the present invention preferably further includes at least one alkaline earth metal oxide selected from among BaO, SrO and CaO in a proportion of about 20% by weight or less relative to the total weight of the glass powder.
The alkaline earth metal oxide serves to decrease the melting temperature in the manufacture of glass and to increase the thermal expansion coefficient of glass. If the content of the alkaline earth metal oxide exceeds about 20% by weight, the resulting insulative ceramic compact may have a decreased Q value.
The glass powder for use in the present invention preferably further includes at least one alkali metal oxide selected from among Li
2
O, K
2
O and Na
2
O in a proportion of about 10% by weight or less, and more preferably from about 2 to 5% by weight, relative to the total weight of the glass powder. The alkali metal oxide serves to decrease the melting temperature in the manufacture of glass. If the content of alkali metal oxide exceeds about 10% by weight, the resulting insulative ceramic compact may have a decreased Q value.
The invented insulative ceramic compact prefe

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