Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2001-05-30
2003-10-07
Lam, Cathy (Department: 1775)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S005000, C501S032000, C501S049000, C501S067000, C501S077000
Reexamination Certificate
active
06630417
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a porcelain composition capable of being fired at a low temperature and is best suited for use in a semiconductor element housing package, a wiring board applied to a multi-layer wiring board or the like, to a porcelain and a method of producing the same, and to a wiring board and a method of producing the same. More particularly, the present invention relates to an improvement of a porcelain which can be fired together with a low-resistance conductor material such as copper, silver or gold and has a low dielectric constant, and also is capable of efficiently dissipating heat generated by the operation of an active element such as semiconductor element, for the purpose of reducing signal delay.
BACKGROUND OF THE INVENTION
Recently, as the information processing technology and communication technology advance in an ever faster rate and are increasingly utilized in everyday life, semiconductor elements are becoming faster in operation and larger in size. As the operation speeds of the semiconductor elements increase, the problem of delay in signal transmission caused by the package, board or the like becomes serious. At the same time, heat resistance of the package and the board poses a significant problem as more heat is generated by the larger semiconductor elements.
In the field of ceramic multi-layer wiring board in the prior art, the most commonly used is an alumina wiring board comprising an insulating layer made of alumina ceramics and a wiring layer made of a high-melting point metal such as tungsten or molybdenum formed on the surface of inside of the insulating layer.
However, in a conventional alumina wiring board, a conductor made of a high-melting point metal such as tungsten (W) or molybdenum (Mo) has a high electrical resistance which, together with the dielectric constant of alumina as high as about 9, results in a significant delay in the signal transmission. For this reason, it has been required to use a low-resistance metal such as copper, silver or gold in place of W or Mo, and decrease the dielectric constant of the insulating layer.
With this background, development efforts have recently been made on wiring boards made of glass ceramics in which the insulating layer is made of glass or glass ceramics which is a composite material of glass and ceramic thereby making it possible to fire the layer at a relatively low temperature of 1050° C. or lower so that a low-resistance metal such as copper, silver or gold which has a low melting point can be used as the conductor, and the dielectric constant can be made lower than that of alumina.
For example, Examined Patent Publication (Kokoku) No. 4-12639 discloses a multi-layer wiring board made by firing an insulating layer made of glass with a SiO
2
filler added thereto and a wiring layer made of a low-resistance metal such as copper, silver or gold simultaneously at a temperature within a range from 900 to 1000° C. Unexamined Patent Publication (Kokai) No. 60-240135 discloses a wiring board made by firing a zinc borosilicate glass with a filler of alumina, zirconia or mullite added thereto together with a metal having a low resistance. Unexamined Patent Publication (Kokai) No. 5-298919 proposes a glass ceramic material wherein mullite or cordierite is precipitated in the crystal phase.
However, the conventional glass ceramic materials such as those described above have a low thermal conductivity within a range from 0.5 to 1.5 W/m·K, resulting in lower heat dissipation property than alumina and other conventional materials. To solve this problem, Unexamined Patent Publication (Kokai) No. 63-307182 and Unexamined Patent Publication (Kokai) No. 4-254477 disclose wiring boards using glass ceramics made by firing AlN of a high thermal conductivity and glass. Unexamined Patent Publication (Kokai) No. 2-196066 discloses a glass ceramic material made by adding an AlN powder having a small particle diameter and an AlN powder having a large particle diameter of not less 2 &mgr;m, forming the mixture into a green body and firing the green body at 950° C.
However, when the non-oxide porcelain such as AlN is used as a filler, the glass and the non-oxide ceramic filler react with each other when fired, and the non-oxide porcelain filler is decomposed to evolve a decomposition gas. This gas has caused such problems as swelling of the porcelain, and degradation in the dimensional accuracy, mechanical strength and water absorption. There has also been such a problem that bubbles are generated in the surface of the porcelain, resulting in rough surface and a metallized wiring layer peeling off. Thus it has been difficult to manufacture satisfactory porcelain consistently, resulting in low yield of production and difficulty in volume production thereof as an industrial product. Since such problems become conspicuous when firing in an oxidizing atmosphere such as air, it has been very difficult to form a wiring layer using copper as the conductor, and the fault of removal of the binder is likely to occur when making wiring with copper.
With the method of mixing the glass powder and the AlN powder and firing the green body, it is difficult to make dense glass ceramics at a firing temperatures of 1050° C. or lower in case the average particle size of the AlN powder is smaller than 2 &mgr;m. This may result in lower mechanical strength of the glass ceramics and/or degradation of the insulation property of the glass ceramics due to water absorption.
Known methods of the AlN powder include the direct nitriding method wherein a metallic Al powder is heated and nitrided at a high temperature of about 2000° C. in a pressurized nitrogen atmosphere, and reducing nitriding method wherein an Al
2
O
3
(alumina) powder with carbon added thereto is nitrided in a nitrogen atmosphere. The reducing nitriding method has such problems that the material cost and the production cost are high, and powder having a large particle diameter cannot be made with high purity. The direct nitriding method, on the other hand, requires processing at a high temperature under a high pressure, and, therefore, the metal Al cannot be completely nitrided with a part of the metal Al being left as an impurity. When much metal Al remains in the porcelain, voids are likely to be formed between the glass and the AlN particles. The voids cause such problems as a decrease in the mechanical strength, lower insulation property due to water absorption by the porcelain, higher dielectric constant and an increase of dielectric loss. Supposed cause of the voids being formed between the glass and the AlN particles is the active property of metal Al which results in reaction with the glass powder during firing, thus evolving a gas.
SUMMARY OF THE INVENTION
A major object of the present invention is to provide a porcelain composition and a porcelain, which are capable of being fired at a low temperature, together with a low-resistance metal such as copper, silver or gold, and have a high thermal conductivity and a low dielectric constant, and a wiring board using the same.
Another object of the present invention is to provide a porcelain and a method of producing the same having an improved yield of production (i.e. high yield of non-defective units), and a wiring board and a method of producing the same.
The porcelain composition capable of being fired at a low temperature comprises 30 to 95% by weight of a borosilicate glass and 5 to 70% by weight of a non-oxide ceramic filler, wherein said borosilicate glass has a glass transition point of 800° C. or lower and a weight loss per unit surface area of said non-oxide ceramics is not more than 0.15 g/cm
2
after dipping said non-oxide ceramic having purity of not less than 96% by weight in a glass melt obtained by melting said borosilicate glass with heating at 1200° C. for five minutes.
The weight loss described above can be used as an index for evaluation of the reactivity between the borosilicate glass and the non-oxide porcelain filler. When the weight loss is within the range de
Iwachi Hiromi
Kawai Shinya
Terashi Yoshitake
Hogan & Hartson
Kyocera Corporation
Lam Cathy
LandOfFree
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