JPH06163311A - Multilayered ceramic capacitor - Google Patents

Abstract

PURPOSE:In a multilayered ceramic capacitor for surface mount for use in general electronic equipment, to solve the problem that when a multilayered ceramic capacitor is soldered to a printed board or the like, mechanical stress is applied to the external electrodes of the multilayered ceramic capacitor through solder by deformation stress or the like in the printed board thereby to produce cracks in the dielectric material below external electrodes, which leads to short-circuit between internal electrodes. CONSTITUTION:The sum of the length L2 of an internal electrode 2a in the direction of an external electrode 3b and the length R2 of a lower external electrode 4b in the direction of an external electrode 3a is made shorter than the distance W between the external electrodes 3a and 3b, and the sum of the length R1 of the internal electrode 2b in the direction of the external electrode 3a and the length L2 of a lower external electrode 4a in the direction of the external electrode 3b is made shorter than a distance W between the external electrodes 3a and 3b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated ceramic capacitor.

[0002]

2. Description of the Related Art FIGS. 7 to 10 show the structure of a conventional monolithic ceramic capacitor.

In FIGS. 7 to 10, reference numeral 1 is a dielectric material in which a plurality of ceramic sheets are laminated, and 2a and 2b are first and second dielectric materials.
The plurality of internal electrodes are alternately laminated via the ceramic sheets inside the dielectric 1. 3a and 3b are first and second
The external electrodes are located on the end face side of the dielectric 1 and are electrically connected to the first and second internal electrodes 2a and 2b, respectively. Further, the lower electrodes 4a and 4b for soldering and fixing to the printed circuit board during use are formed subsequently to the first and second external electrodes 3a and 3b (here, on each surface of the laminated ceramic capacitor). Of these, the surface that should contact the printed circuit board is called the bottom surface.)

In the monolithic ceramic capacitor having the above-described structure, the internal electrodes 2a and 2b are designed to be as large and wide as possible in order to obtain a large size and a size smaller than conventional ones. Further, the lower electrodes 4a and 4b are also designed to be large in order to ensure the soldering connection with the printed circuit board.
That is, in FIG. 7, the length L1 of the first lower surface external electrode 4a in the direction of the second external electrode 3b is long, and the length R1 of the second internal electrode 2b in the direction of the first external electrode 3a is also long. Was longer than the distance W between the first and second external electrodes 3a and 3b.

[0005]

FIG. 10 shows a sectional view of the laminated ceramic capacitor having the above structure soldered to a printed circuit board. The lower surface external electrodes 4a and 4b are opposed to the land 5 of the printed circuit board 8 and are connected by the solder 6. If the soldering conditions are inappropriate during this soldering, the printed circuit board 8 will bend due to the temperature of the solder or the like. The stress of this deflection is represented by F in the figure. When this stress is transmitted to the monolithic ceramic capacitor, the stress concentrates on the end portion (inside) of the lower surface external electrode 4a, and a crack 7 is generated in the dielectric 1 from that portion. Internal electrode 2
Since a and 2b are formed of silver or the like, elongation occurs with respect to tensile stress, and cracks do not occur when the stress is small. That is, due to the crack 7, the internal electrodes 2 facing each other
There is a problem in that a gap is formed between a and 2b, and if moisture penetrates into the gap, a voltage may be applied between the internal electrodes 2a and 2b during operation of the electric circuit to cause a leak in the gap, leading to a short circuit failure. Was there.

The present invention solves the above conventional problems and provides a highly reliable monolithic ceramic capacitor which does not short-circuit due to leakage even when excessive stress is applied to a printed circuit board when soldered. The purpose is to

[0007]

In order to achieve this object, the present invention is directed to the length of the first internal electrode in the direction of the second external electrode and the length of the second lower external electrode in the direction of the first external electrode. Is shorter than the distance between the first and second external electrodes,
The length of the second inner electrode in the direction of the first outer electrode,
The sum of the length of the lower surface external electrode in the direction of the second external electrode is shorter than the distance between the first and second external electrodes.

[0008]

With this structure, even when an unreasonable stress is applied to the laminated ceramic capacitor when it is soldered to the printed circuit board and a crack is generated in the dielectric, the gap of the dielectric formed by the crack running from the end of the lower surface external electrode is It occurs between the internal electrodes on one side (for example, between the first internal electrodes) and does not occur between the opposing first and second internal electrodes, so that the leakage between different electrodes due to the application of the voltage does not occur. High reliability can be obtained without short circuit failure.

[0009]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. 1 to 3, reference numeral 1 is a dielectric formed by laminating a plurality of ceramic sheets.
Reference numerals 2a and 2b denote first and second internal electrodes, which are made of a material such as silver or palladium and have a thickness of about 3 microns.
The ceramic sheets having a thickness of about 15 microns are alternately laminated. Reference numerals 3a and 3b denote first and second external electrodes, which are located on the end face portion of the dielectric 1 and electrically connected to the first and second internal electrodes 2a and 2b, respectively. Further, lower surface external electrodes 4a, 4b for soldering connection and fixing to a printed board at the time of use are formed following the first and second external electrodes 3a, 3b.

The overall size is about 3.2 mm × 1.6 mm × height (thickness) 1.2 mm. Of these, 3.2 mm corresponds to the distance W between the external electrodes 3a and 3b on both end surfaces. The length L2 of the first inner electrode 2a in the direction of the second outer electrode 3b is 2.2 mm, and the length R2 of the second lower surface outer electrode 4b in the direction of the first outer electrode 3a is 0.5 mm. And the sum of L2 and R2 is 2.7 mm, and W is 3.2 mm
Is shorter than. Similarly, the length R1 of the second inner electrode 2b in the direction of the first outer electrode 3a is 2.2 mm.
The length L1 of the lower surface external electrode 4a in the direction of the second external electrode 3b is 0.5 mm, the sum of L1 and R1 is 2.7 mm, which is shorter than W of 3.2 mm.

The operation of the monolithic ceramic capacitor configured as described above will be described with reference to FIG.
The lower surface external electrodes 4a and 4b are opposed to the land 5 of the printed circuit board 8 and are connected by the solder 6. If the soldering conditions are inappropriate during this soldering, the printed circuit board 8 will bend due to the temperature of the solder or the like. The stress of this deflection is represented by F in the figure. When this stress is transmitted to the monolithic ceramic capacitor, the stress is the bottom external electrode 4a.
Concentrate on the end (inner side), and cracks 7 occur in the dielectric 1 from that portion. Since the internal electrodes 2a and 2b are made of silver or the like, they are elongated with respect to the tensile stress, so that cracks do not occur when the stress is small. Although the mechanism up to this point is similar to that of the conventional example, in the present embodiment, the crack 7 occurs between the internal electrodes 2a and does not reach the opposing internal electrode 2b. Therefore, no voltage is applied between the first and second internal electrodes 2a and 2b sandwiching the void of the crack 7, and therefore current leakage does not occur, and the performance as a capacitor is maintained as it is. The voltage applied between the electrodes at the time of circuit operation does not cause a leak in the air gap to cause a short-circuit defect, resulting in high reliability.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 5 is a cross-sectional view in which the laminated ceramic capacitor of the second embodiment is attached to a printed circuit board, and the reference numerals and the like in the drawing are omitted for the same components as those described in the above embodiments. The length of the second inner electrode 2b in the direction of the first outer electrode 3a is such that the length R12 on the lowermost surface side is longer than the length R11 on the uppermost surface side, and gradually decreases from the lower surface side to the upper surface side. Has become. The same relationship holds for the first internal electrode 2a.

Consider a case where cracks 7 are formed in the monolithic ceramic capacitor constructed as described above. Generally, when the crack progresses from the end portion of the lower surface external electrode 3a or 3b to the upper surface side, it progresses vertically right above, but rarely, it may progress obliquely. Even when the crack progresses diagonally, the first and second internal electrodes 2
Since the lengths of a and 2b are gradually shortened toward the upper surface, cracks do not reach the opposing internal electrodes 2b or 2a, and short-circuit failure of the laminated ceramic capacitor can be prevented.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 6 is a cross-sectional view in which the laminated ceramic capacitor of the third embodiment is attached to a printed board, and the reference numerals and the like in the drawing are omitted for the same components as those described in the above embodiments. Regarding the length of the second inner electrode 2b in the direction of the first outer electrode 3a, the length R13 of the central portion thereof is longer than the length R11 of the upper and lower surfaces thereof, and the length from the central portion to the upper and lower surfaces is increased. It becomes shorter as you go. The same relationship holds for the first internal electrode 2a.

Consider a case where cracks 7 are formed in the monolithic ceramic capacitor constructed as described above. Generally, when the crack progresses from the end portion of the lower surface external electrode 3a or 3b to the upper surface side, it progresses vertically right above, but rarely, it may progress obliquely. The structure in which the length of the internal electrode 2b is devised so as to escape from the crack when the crack progresses obliquely is the same as that of the second embodiment. It has a structure that takes into consideration the circumstances when it is mounted in No. 8.

That is, although the lower surface of the monolithic ceramic capacitor has been defined as the surface that contacts the printed circuit board 8, discussion has been proceeded. In the case of taping packaging or stick packaging, the front and back surfaces (upper surface and lower surface) are specified. Printed circuit board 8
However, it is possible that the front and back sides cannot be specified when mounting on a printed circuit board in bulk packaging. Even when the upper surface and the lower surface in this case are mounted reversely, in this embodiment, the internal electrodes are short on both the upper surface side and the lower surface side, so that the structure escapes from the cracks, and therefore the occurrence of short circuit failure is prevented. It can be prevented.

[0017]

As described above, according to the present invention, the sum of the length of the first internal electrode in the direction of the second external electrode and the length of the second lower surface external electrode in the direction of the first external electrode is calculated as follows. Shorter than the distance W between the first and second external electrodes, the length of the second internal electrode in the direction of the first external electrode, and the length of the first lower surface external electrode in the direction of the second external electrode. By making the sum shorter than the distance between the first and second external electrodes, even when unreasonable stress is applied to the laminated ceramic capacitor when soldering it to the printed circuit board and cracks occur in the dielectric, Since the void of the dielectric formed by the crack running from the end of the lower surface external electrode is generated between one internal electrode (for example, between 2a), it is not generated between the opposing internal electrodes (between 2a and 2b), Leakage between different poles caused by voltage application does not occur, thus short circuit failure It is not enough, in which it is possible to obtain high reliability.

Further, by changing the length of the internal electrode depending on the upper surface side, the lower surface side, and the central portion, the above object can be achieved with respect to various cracks.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a monolithic ceramic capacitor according to an embodiment of the present invention.

FIG. 2 is a plan view of a monolithic ceramic capacitor according to an embodiment of the present invention.

FIG. 3 is a front sectional view of a monolithic ceramic capacitor according to an embodiment of the present invention.

FIG. 4 is a front sectional view for explaining an operation in a flexed state of the printed circuit board when the multilayer ceramic capacitor according to the embodiment of the present invention is soldered to the printed circuit board.

FIG. 5 is a front sectional view of a monolithic ceramic capacitor according to another embodiment of the present invention.

FIG. 6 is a front sectional view of a monolithic ceramic capacitor according to still another embodiment of the present invention.

FIG. 7 is a partially cutaway perspective view of a conventional monolithic ceramic capacitor.

FIG. 8 is a plan view of a conventional monolithic ceramic capacitor.

FIG. 9 is a front sectional view of a conventional monolithic ceramic capacitor.

FIG. 10 is a front cross-sectional view for explaining an operation in a flexed state of a printed circuit board when a conventional monolithic ceramic capacitor is soldered to the printed circuit board.

[Explanation of symbols]

 1 Dielectric 2a, 2b 1st, 2nd internal electrode 3a, 3b 1st, 2nd external electrode 4a, 4b 1st, 2nd lower surface external electrode 5 Land 6 Solder 7 Crack 8 Printed circuit board

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masafumi Hanatani 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A dielectric body formed by laminating a plurality of ceramic sheets, and first and second dielectric layers formed on both ends of the dielectric body.
A second external electrode and first and second electrodes provided on the lower surface of the dielectric and electrically connected to the first and second external electrodes, respectively.
A second lower surface external electrode and a plurality of first and second internal electrodes which are alternately laminated inside the dielectric through the ceramic sheet and are connected to the first and second external electrodes, respectively. And the sum of the length of the first inner electrode in the direction of the second outer electrode and the length of the second lower surface outer electrode in the direction of the first outer electrode is The sum of the length of the second inner electrode in the direction of the first outer electrode and the length of the first lower surface outer electrode in the direction of the second outer electrode is shorter than the distance between the outer electrodes, and A laminated ceramic capacitor shorter than the distance between the second external electrodes. 2. The length of the first internal electrode in the direction of the second external electrode is shortened as it moves from the lower surface side to the upper surface side, and the length of the second internal electrode in the first external electrode direction. The multilayer ceramic capacitor according to claim 1, wherein the length is shortened as it moves to the upper surface side. 3. The length of the first inner electrode in the direction of the second outer electrode is shortened as it moves from the central portion to the upper side and the lower surface side, and the length of the second inner electrode in the direction of the first outer electrode is reduced. Length,
The length is shortened as moving from the central portion to the upper side and the lower side.
The multilayer ceramic capacitor described.