Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-07-26
2003-12-09
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306300
Reexamination Certificate
active
06661641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic ceramic capacitor, and more particularly to a monolithic ceramic capacitor having a structure in which terminal members each comprising a metal plate are bonded to external electrodes.
2. Description of the Related Art
In general, monolithic ceramic capacitors have a rectangular shape, and are provided with external electrodes at the opposite ends thereof, respectively. Ordinarily, when such a monolithic ceramic capacitor is mounted onto an appropriate wiring substrate, the above-mentioned external electrodes are soldered directly to a predetermined conduction land on the wiring substrate whereby the monolithic ceramic capacitor is surface-mounted.
However, when the mounting is carried out by soldering the external electrodes directly onto the wiring substrate as described above, mechanical damage may be caused in the monolithic ceramic capacitor. That is, the capacitor body may be cracked or the external electrodes may be peeled from the capacitor body.
In many cases, such mechanical damage is caused, e.g., by a stress based on shrinkage occurring when solder for connection is solidified, or by a stress produced by a difference between the thermal expansion coefficients of the wiring substrate and the monolithic ceramic capacitor, or by a stress produced by the deflection of the wiring substrate.
These problems have been practically solved by a monolithic ceramic capacitor having external electrodes to which terminal members each comprising a metal plate are attached. In monolithic ceramic capacitors having such a structure, advantageously, a stress which causes the above-described mechanical damage can be mostly absorbed in the metal plates constituting the terminal members, which are distorted in response to the deflection. Accordingly, there is hardly any mechanical damage to the monolithic ceramic capacitors.
Ordinarily, the above-described terminal members are bonded to the external electrodes with a conductive bonding material, for example, solder, with specific faces of the terminal members being opposed to the external electrodes.
However, a monolithic ceramic capacitor having the terminal members bonded thereto as described above may encounter the following new problems.
In particular, when a monolithic ceramic capacitor containing barium titanate type ceramic as a dielectric is used in a high voltage or high frequency range, electrostriction tends to be generated, which is caused by piezoelectric phenomena in the dielectric in the capacitor body. A stress caused by such electrostriction is especially great in high capacitance monolithic ceramic capacitors.
When electrostriction occurs as described above, the displacement of the capacitor body caused by the electrostriction is considerably constrained by the terminal members which are bonded to the external electrodes, with the faces of the terminal members being opposed to the faces of the external electrodes. Therefore, the stress produced by the electrostriction can hardly escape.
As a result, the stress caused by the electrostriction is applied repeatedly and is concentrated on the bonding portions between the terminal members and the external electrodes. Fatigue breaking may occur in the bonding portions. In the worst case, cracks may be formed in the dielectric ceramic portion of the capacitor body. Even if such breaking or the like does not occur, the electrostriction can be transmitted to a wiring substrate or the like, resulting in resonance, which causes a phenomenon called “creaking” in some cases.
SUMMARY OF THE INVENTION
The present invention, however, can provide a monolithic ceramic capacitor which can solve the above-described problems.
To solve the above-described technical problems, according to the present invention, there is provided a monolithic ceramic capacitor which comprises a chip capacitor body having external electrodes formed on the opposite end faces thereof, and plural internal electrodes formed in lamination so that each is electrically connected to a predetermined one of the external electrodes, and terminal members each formed of a metal plate bonded to a respective one of the external electrodes with a conductive bonding material. Each terminal member has a protuberance which projects toward the external electrode so that the bonding portion where the terminal member is bonded to the external electrode extends substantially linearly along a part of the external electrode.
According to the present invention, preferably, the direction in which the bonding portion is elongated substantially linearly is selected to be substantially parallel to the internal electrodes.
In the preferable form described above, the width of the bonding portion is preferably up to ⅔, more preferably up to {fraction (4/9)}, and most preferably up to ⅓ of the size of the end face of the capacitor body, the size being measured in the lamination direction of the internal electrodes.
Further, in the above-described preferred forms, preferably, the center in the width direction of the bonding portion is positioned in the range of ⅕ to ⅘, more preferably {fraction (2/8)} to {fraction (6/8)}, and still more preferably ⅜ to ⅝ of the size of the end face from one side edge of the end face of the capacitor body in the lamination direction of the internal electrodes, the size being measured in the lamination direction of the internal electrodes.
According to the present invention, in a specific form, the protuberance is formed so as to be elongated continuously linearly. In this case, the protuberance may be formed by a bending line of a metal plate constituting the terminal member.
In another specific form of the present invention, the protuberance may be formed of plural protuberances which are distributed substantially linearly.
Further, the present invention may be applied to a monolithic ceramic capacitor provided with plural capacitor bodies. In this case, the terminal members are attached to the respective external electrodes of the plural capacitor bodies in common.
Moreover, the monolithic ceramic capacitor of the present invention may be provided with a case for accommodating the capacitor body while the terminal elements partially project outside. In the above instance, preferably, positioning pieces for positioning the capacitor body in the case are integrally formed in the terminal members.
Further, according to the present invention, there is provided a monolithic ceramic capacitor which comprises a chip capacitor body having external electrodes formed on the opposite end faces thereof, and plural internal electrodes formed in lamination so that each is electrically connected to a predetermined one of the external electrodes, respectively, and terminal members formed of a metal plate bonded to a respective one of the external electrodes, each terminal member having plural terminal elements arranged so as to be distributed at intervals in the width direction of the external electrode, the plural terminal elements being so constructed that each terminal element positioned at the ends in the arrangement direction has a lower constraining degree being defined as a degree of constraint of a stress produced by the electrostriction phenomenon in of the capacitor body, which is attributed to the bonding of the terminal elements to the external electrodes.
Further, the present invention has been devised based on the knowledge that the ratio of the displacement of a capacitor body occurring when electrostriction in an area mode is generated in a monolithic ceramic capacitor is zero at the center in the width direction of an external electrode, and becomes larger at a position more distant from the center. As described above, the present invention aims at reducing effects of a stress caused by electrostriction by dividing each terminal member into plural terminal elements, and constructing the plural terminal elements so that each terminal element positioned at an end in the a
Kubota Yasuhiko
Moriwaki Nobushige
Nishiyama Shigeki
Watanabe Ken'ichi
Yoshida Kazuhiro
Reichard Dean A.
Thomas Eric
LandOfFree
Monolithic ceramic capacitor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Monolithic ceramic capacitor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Monolithic ceramic capacitor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3113300