Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2002-06-14
2004-11-16
Jones, Deborah (Department: 1775)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C510S328000
Reexamination Certificate
active
06818574
ABSTRACT:
TECHNICAL FIELD
This invention relates to a jointed body of glass-ceramic and aluminum nitride sintered body and method for producing the jointed body.
BACKGROUND ART
Recently, use of microwave of 1 GHz, such as microwave band and quasimillimetric wave band, is increasing in the field of wireless communication, e.g., portable telephones, and optical communication.
As semiconductors operated in such a high-output, high-power consumption Ga—As FET, Si—Ge HBT, CMOS or GaN laser diode and the like are started to be used. Electric circuits on which such semiconductors are to be mounted must meet such requirements as 1) that the circuit pattern material shows small electric resistance, 2) that multi-layered circuit can be formed for size reduction, 3) that the substrate insulation material has a high heat conductivity, high electric insulation and desirably low dielectric constant, and 4) that environmental pollution by circuit substrate material is little.
However, there is no single insulating substrate material meeting all of these conditions. Multi-layered circuit substrate using a highly thermoconductive aluminium nitride sintered body is available, but its electric circuit conductor is made of tungsten/molybdenum type material having high electric resistance and is unsuitable for high-frequency circuits.
A conceivable realistic solution of above problem is a composite circuit substrate in which aluminum nitride sintered body is joined with glass. That is, aluminum nitride sintered body functions to spread the heat from semi-conductors, and further in which a part of an electric circuit is formed; a mono-layered or multi-layered glass layer is formed thereon using paste-printing technique or the like: and an electric circuit is formed with Au-, Ag-, or Cu-derived low resistance material on the surface or inside of said glass layer.
A glass material for realizing such a circuit substrate must possess such properties as: 1) high electrical insulation and favorable dielectric characteristics, 2) thermal expansion coefficient close to that of aluminum nitride sintered body, 3) direct jointability with aluminum nitride sintered body, not mediated by an oxide film, 4) inclusion of crystallized phase to enable repeated sintering, and 5) relatively low jointing temperature with aluminum nitride sintered body, which must not be higher than the melting point of the metal component of Au-, Ag- or Cu-metallized material, specifically, not higher than 1100° C., in other words, the operation temperature for softening the glass to achieve sufficiently intimate jointing with aluminum nitride sintered body must not be higher than 1100° C.
As low temperature-softening glass, those containing lead oxide can be produced with relative ease, but lead-containing glass is fundamentally toxic and significantly adversely affects terrestrial environments, although lowering in softening point can be easily achieved therewith. Furthermore, lead-containing glass is apt to have a high thermal expansion coefficient. It also has a defect of readily inducing foaming phenomenon under high temperatures at which it reacts with aluminum nitride sintered body and the reaction gas remains in the glass.
As glass materials for the circuit substrates, those which are described in JP-A-340443/1994 and JP-B-68065/1995 are known. The glass in JP-A-340443/1994 contains a large amount of titanium or zirconium and lead, and the defect of higher thermal expansion coefficient than that of aluminum nitride sintered body, which is 4.5×10
−6
/° C., is not fully removed. The glass also exhibits low joining strength with aluminum nitride substrate. The glass in JP-B-68065/1005 exhibits favorable thermal expansion coefficient and electric insulation, but requires a high temperature treatment at 1100-1500° C. for obtaining satisfactory jointability with aluminum nitride. Therefore, two or more steps are necessary for incorporating an electric circuit therein.
The present invention is made for solving such problems as above-described. I noticed an anorthite (CaO.Al
2
O
3
.2SiO
2
) sintered body has, as taught in an article by R. A. Gdula,
American Ceramic Society Bulletin,
1971, Vol.50, No.6, 555-557, a high electric insulation (2.8×10
15
&OHgr;.cm: 25° C.), a small dielectric constant (6.2: 1 MHz, 25° C.), a thermal expansion coefficient (48×10
−7
/° C.: 150° C.-700° C.) which is close to that of aluminum nitride sintered body, and furthermore stability in reducing atmosphere such as of H
2
, and conducted concentrative studies thereof.
In consequence, I discovered amorphous glass which contains Ca, Si and Al components and hence is expected to be crystallized into anorthite crystals under heating has low melting point in the absence of a large amount of Pb component, exhibits good jointability with aluminum nitride sintered body at relatively low temperatures not higher than 1100° C. and crystallizes under heating to separate a crystal component having a characteristic strongest line in a range of 2&THgr;=27.6°-28.2° in powder X-ray diffraction using CuK&agr; line. Moreover, I also found that the crystallized glass or glass-ceramic containing said crystal component possessed not only those characteristic properties attributable to said anorthite sintered body but also high thermal stability well withstanding repeated heating for forming a multi-layered glass. (In the following, an amorphous glass having the composition as will form the crystals showing the strongest line in a range of 2&THgr;=27.6° to 28.2° under heating may occasionally be referred to as “starting glass”.
I furthermore found that use of Zn component-containing glass as the starting glass could further lower the crystallization temperature of the crystals having the strongest line in a range of 2&thgr;=27.6° to 28.2° in powder X-ray diffraction using CuK&agr; line, by 25-100° C. or even more, and could also sharpen the separation pattern of said crystals. It was whereby made possible to prepare a jointed body of glass-ceramic with aluminum nitride sintered body at still lower temperatures, with less occurrence of swelling or residual. carbon in so produced glass-ceramic.
Moreover, I also found that a glass of above-described composition could be sufficiently crystallized, without containing a large amount of Ti or Zr component as nucleating agent and hence the glass-ceramic prepared therefrom could have a thermal expansion coefficient nearly the same to that of aluminum nitride sintered body.
DISCLOSURE OF THE INVENTION
Namely, the present invention provides a jointed body of glass-ceramic consisting of crystalline portion and amorphous portion with aluminum nitride sintered body, which is characterized in that the crystalline portion contains as main crystals a crystal having the strongest line in a range of 2&thgr;=27.6° to 28.2° in powder X-ray diffraction using CuK&agr; line and said glass-ceramic contains 0.5-30% by weight of a Zn component in terms of oxide, not more than 10% by weight of the sum of a Ti component and Zr component in terms of respective oxides and not more than 5% by weight of a Pb component in terms of oxide.
The invention also provides a method for producing a jointed body of glass-ceramic with aluminum nitride sintered body, which method is characterized by forming a glass layer containing an amorphous glass having a composition of 0.5-30% by weight of a Zn component in terms of oxide, not more than 10% by weight of the sum of a Ti component and Zr component in terms of respective oxides and not more than 5% by weight of a Pb component in terms of oxide, on an aluminum nitride sintered body, heating the resulting composite to a temperature not lower than the softening point of said amorphous glass and whereby crystallizing said glass to convert it to a glass-ceramic, the main crystals therein having the strongest line in a range of 2&thgr;=27.6° to 28.2° in powder X-ray diffraction using CuK&agr; line. The present invention also covers an embodiment of the method for produc
Jones Deborah
Koppikar Vivek
Tokuyama Corporation
Wenderoth , Lind & Ponack, L.L.P.
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