Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-07-11
2004-06-22
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S901000, C428S137000, C428S138000, C501S005000, C501S006000, C501S009000, C501S010000, C501S032000, C336S073000, C174S255000
Reexamination Certificate
active
06753070
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to insulating ceramic compacts for use in multilayer circuit substrates, and more particularly, relates to a high-frequency insulating ceramic compact which is suitably used for a hybrid multilayer circuit substrate for mounting semiconductor elements or various electronic elements thereon and which can be simultaneously fired with a conductive material such as copper or silver, relates to a ceramic multilayer substrate using the insulating ceramic compact and relates to a ceramic electronic device.
2. Description of the Related Art
In recent years, trends toward high speed and high frequency processing of electronic devices have been progressing rapidly. In addition, electronic elements mounted on electronic devices are required to satisfy a higher processing speed and a higher integration density and furthermore, are also required to satisfy a higher mounting density. In response to the requirements described above, multilayer circuit substrates have been used as substrates for mounting semiconductor elements and various electronic elements thereon. In multilayer circuit substrates, conductor circuits or functional electronic elements are embedded, and hence, miniaturization of electronic devices can be performed.
As a material for forming the multilayer circuit substrate described above, alumina has heretofore been used in many cases.
The firing temperature for alumina is relatively high, such as 1,500 to 1,600° C. Accordingly, a high melting point metal, such as molybdenum (Mo), molybdenum-manganese (Mo—Mn), tungsten (W) or the like, must be generally used as a material for a conductive circuit embedded in the multilayer circuit substrate composed of alumina. However, these high melting point metals have high electrical resistance.
Accordingly, it has been strongly desired that an inexpensive metal, such as copper, having a lower resistance than that of the high melting point metals be used as a conductive material. In order to use copper as the conductive material, usage of a glass ceramic or a crystallized glass, which can be fired at 1,000° C. or less, is proposed (for example, Japanese Unexamined Patent Application Publication No. 5-238774).
In addition and in consideration of connection with a semiconductor element such as a silicon (Si) chip, usage of a ceramic having a coefficient of thermal expansion approximately equivalent to that of Si is proposed as a material for a multilayer circuit substrate (Japanese Unexamined Patent Application Publication No. 8-34668).
However, the known substrate materials described above, which can be fired at a low temperature, have problems in that the mechanical strength is low, the Q value is low and the types of the precipitated crystalline phases and the ratio thereof are easily influenced by the firing process.
In addition, the substrate materials disclosed in Japanese Unexamined Patent Application Publications Nos. 5-238774 and 8-34668 have a problem in that co-firing with a high dielectric material having a high coefficient of thermal expansion is difficult to perform.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an insulating ceramic compact which can solve the problems of the conventional techniques described above, can be fired at a low temperature, can be simultaneously fired with a conductive material having a relatively low melting point, such as silver or copper, has a low relative dielectric constant and superior high-frequency characteristics, and in addition, has a high coefficient of thermal expansion.
Another object of the present invention is to provide a ceramic multilayer substrate which is formed of the insulating ceramic compact described above, can be fired at a low temperature, has a low relative dielectric constant and superior high-frequency characteristics and can be obtained by co-sintering with a high dielectric material having a high coefficient of thermal expansion, and is to provide a ceramic electronic device and a laminated ceramic electronic device which use the ceramic multilayer substrate described above.
Through intensive research by the inventors of the present invention in order to solve the problems described above, it was discovered that, in an insulating ceramic compact formed of a fired mixture of an MgAl
2
O
4
-based ceramic and a borosilicate glass, when an MgAl
2
O
4
crystal phase and at least one of an Mg
3
B
2
O
6
crystal phase and an Mg
2
B
2
O
5
crystal phase are precipitated as primary crystal phases, or when an MgAl
2
O
4
crystal phase, an Mg
2
SiO
4
crystal phase and at least one of an Mg
3
B
2
O
6
crystal phase and an Mg
2
B
2
O
5
crystal phase are precipitated as primary crystal phases, an insulating ceramic compact can be obtained having a low relative dielectric constant, superior high frequency characteristics and a high coefficient of thermal expansion, whereby the present invention was made.
In accordance with one aspect of the present invention, an insulating ceramic compact is provided comprising a fired mixture of an MgAl
2
O
4
-based ceramic and a borosilicate glass, in which an MgAl
2
O
4
crystal phase and at least one of an Mg
3
B
2
O
6
crystal phase and an Mg
2
B
2
O
5
crystal phase are precipitated as primary crystal phases.
In accordance with another aspect of the present invention, an insulating ceramic compact is provided comprising a fired mixture of an MgAl
2
O
4
-based ceramic and a borosilicate glass, in which an MgAl
2
O
4
crystal phase, an Mg
2
SiO
4
crystal phase, and at least one of an Mg
3
B
2
O
6
crystal phase and an Mg
2
B
2
O
5
crystal phase are precipitated as primary crystal phases.
In the present invention, the borosilicate glass preferably comprises boron oxide, silicon oxide and magnesium oxide. When an MgAl
2
O
4
ceramic and a glass composition containing at least boron oxide (B
2
O
3
), silicon oxide (SiO
2
) and magnesium oxide (MgO) are combined together, the MgAl
2
O
4
crystal phase and at least one of the Mg
3
B
2
O
6
crystal phase and the Mg
2
B
2
O
5
crystal phase can be precipitated as the primary crystal phases, or the MgAl
2
O
4
crystal phase and at least one of the Mg
2
SiO
4
crystal phase, the Mg
3
B
2
O
6
crystal phase, and the Mg
2
B
2
O
5
crystal phase can be precipitated as the primary crystal phases, whereby, in both cases, an insulating ceramic compact can be obtained having superior high frequency characteristics and a high coefficient of thermal expansion.
The borosilicate glass preferably comprises about 8 to 60 wt % of boron oxide calculated as B
2
O
3
, about 10 to 50 wt % of silicon oxide as SiO
2
and about 10 to 55 wt % of magnesium oxide as MgO. In addition, the borosilicate glass more preferably comprises about 20 to 40 wt % of boron oxide.
In the borosilicate glass, the boron oxide preferably occupies about 8 to 60 wt % in the form of B
2
O
3
. The boron oxide serves primarily as a fusing agent. When the content of boron oxide is less than about 8 wt % in the form of B
2
O
3
, the melting temperature may be excessively increased in some cases and when the content is more than about 60 wt %, the humidity resistance may be degraded in some cases.
The silicon oxide preferably occupies about 10 to 50 wt % in the form of SiO
2
. In addition, the silicon oxide more preferably occupies about 13 to 38 wt %. When the content thereof is less than about 10 wt %, the chemical stability of the borosilicate glass tends to be decreased and when the content is more than about 50 wt %, the melting temperature of the glass may be increased in some cases.
The magnesium oxide preferably occupies about 10 to 55 wt % in the form of MgO. In addition, the magnesium oxide more preferably occupies about 35 to 53 wt %. MgO decreases a melting temperature when a glass is formed and is a constituent component of a crystal in the crystallized glass. In particular, an MgO—B
2
O
3
compound shows a Qf value (product of the Q value and the frequency f) of tens of thousands GHz and is primarily respons
Chikagawa Osamu
Mori Naoya
Sugimoto Yasutaka
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Watkins III William P.
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