Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2001-12-28
2004-04-06
Lam, Cathy (Department: 1775)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S738000, C361S746000, C428S692100
Reexamination Certificate
active
06717794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite multilayered ceramic board in which plural kinds of multilayered ceramic boards are laminated, and to a method of manufacturing the same.
2. Description of the Background Art
As for mobile communication devices such as mobile telephones and portable communication terminals, smaller-sized devices have been highly required. Thus, smaller size and higher performance have also been required for high-frequency circuit boards used as internal components of such devices.
In order to satisfy such requirements, a multilayered ceramic board is employed for the high-frequency circuit board. The multilayered ceramic board has such construction that wiring patterns are formed on green sheets serving as the base of the ceramic board to form capacitance or inductance components thereon, without employing the technique that capacitors or inductors being components for use in surface mount are mounted on a printed circuit board. Since the multilayered ceramic board requires a smaller number of surface mount parts, the smaller-sized high-frequency circuit board is achieved.
The multilayered ceramic board is manufactured by forming wiring patterns on a plurality of green sheets mainly composed of alumina (Al
2
O
3
), laminating those green sheets, and sintering the whole of the laminated sheets at a temperature of from 800° C. to 1600° C. to integrate the sintered sheets as one.
FIGS.
7
(
a
) and
7
(
b
) are schematic perspective views showing a method of manufacturing a conventional multilayered ceramic board.
As shown in FIG.
7
(
a
), first of all, predetermined wiring patterns
32
A to
32
D are formed, respectively, on green sheets
31
A to
31
D composed of alumina by screen printing. Then, as shown in FIG.
7
(
b
), the green sheets
31
A to
31
D are laminated and sintered together at a temperature of from 800° C. to 1600° C. to form a multilayered ceramic board
30
. Here, the green sheets are such sheets as made by mixing and kneading organic binders, ceramic raw material powders and the like, then processing the resultant mixture in the form of sheets and drying the processed sheets.
In the multilayered ceramic board
30
, it is made possible to obtain capacitance or inductance in the internal portion of the multilayered ceramic board by forming the predetermined wiring patterns
32
A to
32
D on the green sheets
31
A to
31
D composed of alumina by screen printing. This makes it possible to reduce the number of capacitors or inductors being the surface mount components, enabling a decrease in the size of the components of the high-frequency circuit. Further, since the multilayered ceramic board
30
is formed of alumina exhibiting an insulation property as a main constituent, the board is suitable for forming resistance therein.
In the case where a multilayered ceramic board made of alumina with a smaller dielectric constant is substituted for a capacitor, the value of capacitance incorporated in the multilayered ceramic board is limited. Thus, if the value of capacitance is required to be obtained in a wide range, a capacitor being a component for use in surface mount is required. Alternatively, in the case where a multilayered ceramic board made of alumina without magnetism is substituted for an inductor, the value of inductance incorporated in the multilayered ceramic board is limited. Thus, if the value of inductance is required to be obtained in a wide range, an inductor or a transformer being a component for use in surface mount is required.
For example, if the value of capacitance and the value of inductance are required in a wide range, the number of components for use in surface mount can further be reduced by using a combination of a multilayered ceramic board composed of dielectric ceramics (hereinafter abbreviated as a dielectric multilayered ceramic board) and a multilayered ceramic board composed of magnetic ceramics (hereinafter abbreviated as a magnetic multilayered ceramic board) rather than using a multilayered ceramic board composed of an insulating ceramics (hereinafter abbreviated as an insulating multilayered ceramic board). A description will now be made on a method of combining the dielectric multilayered ceramic board and the magnetic multilayered ceramic board.
FIGS.
8
(
a
) and
8
(
b
) are schematic perspective views showing a manufacturing method of combining the dielectric multilayered ceramic board and the magnetic multilayered ceramic board.
With reference to FIG.
8
(
a
), wiring patterns
42
A to
42
C are first formed on green sheets
41
A to
41
C made of dielectric ceramics by screen printing. Those green sheets are composed of, e.g., barium titanate (with a dielectric constant of 1400) (hereinafter abbreviated as dielectric green sheets). Wiring patterns
44
A to
44
C are formed on green sheets
43
A to
43
C composed of magnetic ceramics by screen printing. Those green sheets are composed of, e.g., a NiZn ferrite (with an initial magnetic permeability>70, a magnetic flux density>0.2T) (hereinafter abbreviated as magnetic green sheets).
Then, with reference to FIG.
8
(
b
), the dielectric green sheets
41
A to
41
C and the magnetic green sheets
43
A to
43
C are laminated integrally, sintered together at a temperature of from 800° C. to 1600° C., so as to form a composite multilayered ceramic board
40
.
In the composite multilayered ceramic board
40
, the wiring patterns
42
A to
42
C formed on the green sheets
41
A to
41
C made of dielectric ceramics constitute a circuit mainly including a capacitance component. The wiring patterns
44
A to
44
C formed on the green sheets
43
A to
43
C made of magnetic ceramics constitute a circuit mainly including an inductance component. This makes it possible to obtain the value of capacitance and the value of inductance in a wide range. This enables a decrease in the number of capacitors and inductors being the components for use in surface mount and enables a decrease in the size of the components for use in the high-frequency circuit.
In the method of forming the composite multilayered ceramic board
40
by integrally laminating the dielectric green sheets
41
A to
41
C and the magnetic green sheets
43
A to
43
C and sintering the laminated sheets in whole, however, an internal stress densification phenomenon occurs which causes shrinkage of the materials for use in the multilayered ceramic boards, in a process that powders of the materials for use in the plurality of multilayered ceramic boards made of different materials are sintered in whole and grow to crystal grains. The shrinkage of the materials vary depending on the type, the thickness and the materials of the green sheets, and the mixing ratio of binders, the particle size and the shape of the material powders or the sintering conditions and the like.
FIG. 9
is a schematic cross-sectional view of the composite multilayered ceramic board
40
showing the sintering state of the board
40
having different shrinkage percentages. With reference to
FIG. 9
, the composite multilayered ceramic board
40
is formed of a dielectric multilayered ceramic board
41
and a magnetic multilayered ceramic board
43
. Since this composite multilayered ceramic board
40
is formed by integrally laminating the dielectric multilayered ceramic board
41
and the magnetic multilayered ceramic board
43
which have different shrinkage percentages and then sintering the laminated boards in whole, deflection R is produced due to the shrinkage of materials.
FIG. 10
is an enlarged view of a joint portion of the dielectric multilayered ceramic board
41
and the magnetic multilayered ceramic board
43
shown in FIG.
9
. With reference to FIG.
10
(
a
), if no deflection R is caused by the shrinkage of materials, ideally, for example, no deviation is produced between a wiring pattern
42
C formed on a dielectric multilayered ceramic board
41
C and a via hole
44
A formed on a magnetic multilayered ceramic board
43
A. However, as shown in FIG.
10
(
Takahashi Seiichirou
Yoshikawa Hideki
Lam Cathy
Sanyo Electric Co,. Ltd.
Westerman Hattori Daniels & Adrian LLP
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