Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-10-15
2001-08-07
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C501S005000, C501S032000
Reexamination Certificate
active
06270880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystalline glass composition for use as an electrical insulator in a circuit board such as a multilayer circuit board, a sintered crystalline glass obtained by firing the crystalline glass composition, an insulator composition containing a crystalline glass powder comprising the crystalline glass composition and a ceramic powder, an insulating paste prepared by mixing the insulator composition and an organic vehicle and a thick film circuit board having an insulating layer obtained by firing the insulating paste.
More specifically, the present invention relates to an improved method for allowing the crystalline glass composition or the insulating paste to be sintered at a low temperature while endowing the sintered crystalline glass or insulating layer obtained by firing them with a low dielectric constant and a high thermal expansion coefficient.
2. Description of the Related Art
Miniaturization and high integration of various kinds of electronic appliances have been aggressively advanced in recent years as a result of developments in semiconductor elements for integrated circuits such as ICs and LSIs. Consequently, miniaturization and high integration are also required for circuit boards for mounting the semiconductor elements for the integrated circuits, forcing the electrical wiring of the circuit board to be fine and multilayered.
It is known that signals propagating in a conductor are usually more delayed when materials surrounding the conductor have higher dielectric constants. Therefore, the electrical insulator material for high speed propagation is required to have a low dielectric constant.
However, since the thermal expansion coefficient of the low dielectric constant insulator is in general smaller than thermal expansion coefficient of conductors for use, for example, in electrodes, it is a problem that deformation and cracks are generated due to differences in the thermal expansion coefficients when various materials are integrated into multilayers.
In relation to the problem described above, Japanese Unexamined Patent Publication No. 3-4594 proposes to construct an insulating layer having a larger thermal expansion coefficient by using principal components of MgO, SiO
2
and CaO in a specified composition ratio in order to manufacture a capacitor-integration type composite circuit board in which a dielectric layer having a large thermal expansion coefficient is integrated by inserting it between insulating layers, thereby increasing the thermal expansion coefficient of the insulating layer. A principal crystalline phase forsterite (Mg
2
SiO
4
) is deposited by calcining at a temperature of 1000° C. to 1300° C. followed by firing at a temperature of 1240° C. to 1340° C. in the insulating layer is disclosed in this publication to increase the thermal expansion coefficient.
However, sintering at a temperature of 1100° C. or less is impossible in the electrical insulators constituting the insulating layers described in the publication above. Therefore, the materials cannot be used for the electrical insulators for the circuit boards in which conductors containing, for example, silver are formed on the surface or inside of them.
Since merwinite (Ca
3
MgSi
2
O
8
), monticellite (CaMgSiO
4
) and calcium silicate (at least one of CaSiO
3
, Ca
3
Si
2
O
7
, Ca
2
SiO
4
and Ca
3
SiO
5
) are known to be crystalline phases having larger thermal-expansion coefficients than forsterite (Mg
2
SiO
4
), the electrical insulators for the insulating layers described in the foregoing publication seem to fall within a composition region where relatively a small amount of these crystalline phases are deposited.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a crystalline glass composition for use in a circuit board in which at least one kind of the crystalline phase among merwinite (Ca
3
MgSi
2
O
8
), monticellite (CaMgSiO
4
) and calcium silicate (at least one of CaSiO
3
, Ca
3
Si
2
O
7
, Ca
2
SiO
4
and Ca
3
SiO
5
), which can be fired at a temperature of 1100° C. or less besides having a larger thermal expansion coefficient than forsterite (Mg
2
SiO
4
), are allowed to be efficiently deposited at a low temperature of 1100° C. or less, thus obtaining an electrical insulator for use in a circuit board having a relative dielectric constant of as low as 12 or less and a thermal expansion coefficient of as high as 10 ppm/° C., and a sintered crystalline glass obtained by firing the crystalline glass composition.
Another object of the present invention is to provide an insulator composition containing the crystalline glass composition described above and a ceramic power, an insulating paste prepared by mixing the insulator composition with an organic vehicle, and a thick film circuit board obtained by firing the insulating paste. More specifically, the object of the present invention is to provide an insulator composition and insulating paste that can be sintered at a temperature of 1100° C. or less while allowing at least one kind of the crystalline phase among merwinite (Ca
3
MgSiO
8
), monticellite (CaMgSiO
4
) and calcium silicate (at least one of CaSiO
3
, Ca
3
Si
2
O
7
, Ca
2
SiO
4
and Ca
3
SiO
5
) to be efficiently deposited at a low temperature of 1100° C. or less as described above, thereby providing an electrical insulator for use in a circuit board having a relative dielectric constant of as low as 10 or less and a thermal expansion coefficient of as high as 8 ppm/° C. after firing, and to provide a thick film circuit board having an insulating layer obtained by firing the insulating paste.
In one first aspect, the present invention provides a crystalline glass composition for use in a circuit board containing SiO
2
, MgO and CaO, the composition ratio of SiO
2
, MgO and CaO represented by % by weight falling within an area surrounded by the lines connecting the points A (25, 45, 30), B (25, 0, 75), C (44, 0, 56), D (44, 22, 34), E (40, 19, 41) and F (29, 40, 31) in a ternary phase diagram, wherein at least one crystalline phase of merwinite, monticellite and calcium silicate are deposited by heat-treating the composition.
The present invention also provides a crystalline glass composition for use in a circuit board in which the composition ratio of SiO
2
, MgO and CaO represented by % by weight% falling within an area surrounded by the lines connecting the points G (30, 19, 51), H (30, 5, 65), I (44, 5, 51), and J (44, 19, 37) in a ternary phase diagram, wherein at least one crystalline phase among merwinite, monticellite and calcium silicate are deposited by heat-treating the composition.
In another aspect, the present invention provides a crystalline glass composition for use in a circuit board containing principal components of SiO
2
, MgO and CaO while containing sub-components of at least one of (1) Al
2
O
3
, (2) at least one of BaO and SrO, and ZnO, (3) at least one of Li
2
O, Na
2
O and K
2
O, and (4) B
2
O
3
, the composition ratio of SiO
2
, MgO and CaO in the principal component represented by % by weight falling within an area surrounded by the lines connecting the points A (25, 70, 5), B (25, 0, 75), C (44, 0, 56) and D (44, 51, 5) in a ternary phase diagram, wherein the sub-component is contained in a combined proportion of about 0.5 to 50 parts by weight relative to 100 parts by weight of the principal component while containing sub-components of (1) about 0.5 to 25 parts by weight of Al
2
O
3
, if any, (2) about 0.5 to 10 parts by weight of at least one of BaO and SrO and ZnO, if any, (3) about 0.5 to 5 parts by weight of at least one of Li
2
O, Na
2
O and K
2
O, if any, and (4) about 0.5 to 25 parts by weight of B
2
O
3
, if any, at least one crystalline phase among merwinite, monticellite and calcium silicate being made to deposit by heat-treating the composition. With this composition, the sintering temperature can be reduced further.
The crystalline glass composition for use in a circuit board as just described above is select
Kawakami Hiromichi
Sunahara Hirofumi
Takagi Hiroshi
Tanaka Toshiki
Watanabe Shizuharu
Lam Cathy
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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