Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1999-03-30
2001-04-17
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S308100, C361S310000
Reexamination Certificate
active
06219220
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic electronic component and a method for producing the same, and especially to improvement in the structure of terminal electrodes provided with a chip of the main ceramic electronic component and to a method for producing the ceramic electronic component provided with such terminal electrodes.
2. Description of the Related Art
Examples of the ceramic electronic component provided with a chip of the main electronic component composed of a ceramic concerned with the present invention include a capacitor, a resistor, an inductor and a filter. These ceramic electronic components are mostly packaged on an appropriate wiring board.
In most ceramic electronic component packaged on the surface, an inner wiring is formed inside of the main electronic component and respective terminal electrodes are formed on at least on each side face of the main electronic component. Such ceramic electronic component is usually packaged by soldering the foregoing terminal electrodes to a given conductive land on the wiring board.
The ceramic electronic component suffers a deformation pulling toward each terminal electrode due to stress generated by shrinkage caused by solidifying solder. Consequently, mechanical damage such as crack formation in the main electronic component appears in the ceramic electronic component.
The mechanical damage in the ceramic electronic component is particularly liable to occur when the ceramic electronic component is packaged on a wiring board comprising aluminum which has good heat releasing property. Since the difference in heat expansion coefficient between the aluminum board and the ceramic electronic component is relatively large, cracks are generated in the main electronic component or in the solder fillet as a result of a repeated temperature increase and temperature decrease cycles.
This sort of mechanical damage is especially liable to be caused when a laminated ceramic capacitor of a high capacitance Pb based dielectric ceramic is packaged on the wiring board because the anti-fracture strength of the board is relatively weak.
For solving the foregoing problems, Japanese Unexamined Patent Publication No. 8-162359 proposes to relax the stress on the main electronic component applied via the terminal electrodes by making the terminal electrodes as a dual layer structure together with providing the inner layer with a porous structure.
However, the ceramic electronic component provided with the terminal electrodes having the dual layer structure described above still involves the following problems. The inner wiring formed inside of the main electronic component and the inner electrodes of a laminated ceramic capacitor, for example, should be electrically connected to the terminal electrodes whose inner layer serves to keep electrical continuity in the terminal electrodes having the dual layer structure described above. However, since this inner layer assumes a porous structure, it sometimes fails to keep sufficient electrical continuity with the inner wiring. Such insufficient electrical continuity becomes more evident as the laminated ceramic capacitor is made to be more compact.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a ceramic electronic capacitor directed to solving the foregoing problems and a method for producing the same.
In a first aspect, the present invention provides a ceramic electronic component provided with a chip of a main electronic component in which inner wiring has been formed and terminal electrodes formed on the outer surface of the main electronic component so as to be electrically connected to the inner wiring, wherein the terminal electrodes is provided with a first layer formed on the outer surface of the main electronic component, a second layer formed at outside of the first layer and a third layer formed at outside of the second layer, the second layer having a porous structure.
Preferably, the second layer contains conductive particles with a particle size of about 3 to 6 &mgr;m
More preferably, the first and third layers contain conductive particles with a particle size of about 0.5 to 2 &mgr;m and the second layer contains conductive particles with a particle size of about 0.5 to 2 &mgr;m and conductive particles with a particle size of about 3 to 6 &mgr;m.
In accordance with another aspect of the present invention, the method for producing a ceramic electronic component comprises the steps of preparing the main electronic component; forming a first conductive paste film containing conductive particles to be formed into the first layer by baking on the outer surface of the main electronic component; forming a second conductive paste layer containing conductive particles to be formed into the second layer by baking and an additive to be burnt out by baking at outside of the first conductive paste film; forming a third conductive paste layer containing conductive particles to be formed into the third layer by baking at outside of the second conductive paste film; and baking the first, second and third conductive paste films.
Further, the amount of the additive in the second conductive paste film may be controlled in order to adjust the void ratio in the porous structure of the second layer.
Also, it is preferable that a step for drying the second conductive paste film is further provided prior to the step for forming the third conductive paste film, wherein the second conductive paste film is baked simultaneously with the third conductive paste.
Gelatin, cellulose or carbon is advantageously used as the additive described above.
REFERENCES:
patent: 4701827 (1987-10-01), Fujikawa et al.
patent: 5561587 (1996-10-01), Sanada
patent: 2118366A (1983-10-01), None
patent: 2272433A (1984-05-01), None
patent: 8162359 (1996-06-01), None
JAPIO Abstract No. 03885507 & JP4250607 A (Taiyo Yuden) 07.09.92.*
JAPIO Abstract No. 03885507 & JP4250607 A (Taiyo Yuden) 07.09.92.
JAPIO Abstract No. 03527310 & JP3190210 A (Matsushita) 20.08.91.
JP 3-190210 A (Matsushita Electric Ind. Co. Ltd.); Patent Abstracts of Japan, vol. 15, No. 448 (E-1133), 1991.11.14 (abstract).
JP 4-250607 A (Taiyo Yuden Co., Ltd.); Patent Abstracts of Japan, vol. 17, No. 28 (E-1308), 1993.01.19 (abstract).
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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