Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-01-30
2002-09-10
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C174S258000, C252S06230Q, C361S321600, C501S032000
Reexamination Certificate
active
06447888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic wiring board equipped with an insulating layer of a high dielectric constant formed of a sintered product of ceramics heaving a high dielectric constant.
2. Description of the Prior Art
A ceramic wiring board used for a package for accommodating semiconductor devices such as LISS is provided with an insulating substrate formed by laminating, in many layers, insulating layers of ceramics such as alumina or mullite, and a metallized wiring layer is arranged on the surface of the insulating substrate or inside therein. In recent years, there has been put into practice a ceramic wiring board forming an insulating substrate by using glass ceramics that can be co-fired with the copper metallize.
In the ceramic wiring board, the number of connection terminals connected to an external circuit board such as printed board tends to increase with an increase in the degree of integration of the semiconductor devices. A ball grid array (BGA) having spherical connection terminals of a solder attached to the lower surface of a ceramic wiring board has been known to be capable of providing the greatest number of connection terminals without increasing the size of the wiring board. In this ball grid array (BGA), the connection terminals are placed and contacted to the wiring conductors formed on an external electric circuit board and are heated at a temperature of 250 to 400° C. so as to melt and connect the connection terminals to the wiring conductors, in order to mount a ceramic wiring board on the external electric circuit board.
Here, the insulating substrate (ceramic wiring board) formed of ceramics such as alumina or mullite has a coefficient of thermal expansion of about 4 to 7×10
−6
/° C. whereas the printed board on which the ceramic wiring board is mounted is, usually, formed of glass-epoxy insulating layer having a coefficient of thermal expansion of about 11 to 18×10
−6
/° C. That is, there exists a large difference in the coefficient of thermal expansion between the external circuit board and the ceramic wiring board. In the mounting structure using the above ball grid array (BGA), therefore, a large thermal stress is generated between the two due to the difference in the coefficient of thermal expansion as heat is generated by the operation of the semiconductor devices. Besides, the effect of this thermal stress increases with an increase in the number of the connection terminals; i.e., the thermal stress is applied to the connection terminals as the operation and stop of the semiconductor devices are repeated, causing the connection terminals to be peeled off the wiring conductors.
Accompanying a rapidly spread use of portable data terminals such as cell phones and notebook personal computers on the other hand, it has been strongly demanded to fabricate electronic parts incorporated therein in small sizes. For example, a switching circuit and a power amplifier circuit of a cell phone are constituted by plural resistors and capacitors that have heretofore been individually placed on the electric circuit board hindering the attempt for decreasing the size and for decreasing the cost of production.
In order to fabricate, in small sizes, the electronic parts incorporated in the portable electronic devices, it is necessary to decrease the size of not only the ceramic wiring hoard for accommodating the semiconductor devices but also of the external circuit board ducts as a printed board for mounting the wiring board. So far, however, the ceramics wiring hoard, capacitor devices and resistor devices have been separately mounted on an external circuit board, making it difficult to decrease the size and driving up the cost for mounting.
Therefore, there has been proposed a capacitor-incorporated board by arranging an insulating layer of a high dielectric constant formed of ceramics having a high dielectric constant inside the ceramic wiring board. However, a composite perovskite dielectric material comprising chiefly BaO—TiO
2
or PbO—TiO
2
which has been known as ceramics having a high dielectric constant, cannot be co-fired with the glass ceramics, and is not suited for the production of a ceramic wiring board having a large coefficient of thermal expansion. Thus, it is very difficult to produce the ceramic wiring board having a small difference of thermal expansion from the external circuit board such as printed board, by using the composite perovskite dielectric material.
In view of the above-mentioned problems, the present applicant has previously proposed a glass ceramic sintered product of high thermal expansion having a high dielectric constant by sintering a glass component of a high thermal expansion and a filler component such as BaTiO
3
or CaTiO
3
. That is, the filler component can be co-fired with the glass component. By using a sintered product of the above glass ceramics, therefore, it is allowed to obtain a ceramic wiring board having a high coefficient of thermal expansion and a small difference in the thermal expansion from the external circuit board such as printed board, effectively avoiding inconvenience caused by the thermal stress that stems from the operation of the semiconductor devices. Further, the sintered product of glass ceramics has a high dielectric constant which makes it possible to obtain a ceramic wiring board of tho type of incorporating a capacitor by using the sintered product of the glass ceramics.
With the sintered product of the glass ceramics, therefore, the sintering is greatly impaired depending upon the filler component such as BaTiO
3
or CaTiO
3
, making it difficult to obtain a densely sintered product at low temperatures and hindering the effort for realizing the practical use.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a ceramic wiring board provided with an insulating layer of a high dielectric constant formed of a sintered product of glass ceramics having a high coefficient of thermal expansion and a high dielectric constant, the ceramic wiring board suited for being reliably mounted an a printed board of an insulating material of an organic resin.
Another object of the present invention is to provide a ceramic wiring board incorporating a capacitor.
According to the present invention, there is provided a ceramic wiring board provided with an insulating layer of a high dielectric constant (high dielectric layer) formed of a ceramic sintered product having a high dielectric constant, wherein said ceramic sintered product contains a crystal phase of lanthanum titanate and a glass phase present on the grain boundaries of said crystal phase, and the ceramic sintered product has a coefficient of thermal expansion at 40 to 400° C. of not greater than 8×10
−6
/° C., a specific inductive capacity at 1 MHz of not smaller than 10, and a porosity of not more than 0.5%.
That is, the high dielectric layer possessed by the ceramic wiring board of the present invention is formed of the ceramic sintered product obtained by firing a filler component containing at least lanthanum titanate together with a glass component of a high thermal expansion. Since the lanthanum titanate is being used, the ceramic sintered product is excellently sintered, is dense, and contains a crystal phase of lanthanum titanate. Besides, a glass phase exists on the grain boundaries of the crystal phase and, hence, the ceramic sintered product exhibits a coefficient of thermal expansion at 40 to 400° C. of not smaller than 8×10
−6
/° C. and a specific inductive capacity at 1 MHz of not smaller than 10. Therefore, even when the ceramic wiring board of the present invention is put to the heat cycle in a state where it is mounted on an external circuit board made of an insulating substrate of an organic resin such as a printed board, generation of a thermal stress due to the difference in the thermal expansion is suppressed and a stably mounted state is maintained for extended period of time
Higashi Masahiko
Kokubu Masanari
Nagae Ken-ichi
Nakao Yoshihiro
Suzuki Shin'ichi
Hogan & Hartson LLP
Kyocera Corporation
Lam Cathy
LandOfFree
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