JPH0749785Y2 - Monolithic ceramic capacitors - Google Patents

Description

[Detailed Description of the Invention] [Industrial application] The present invention relates to a monolithic ceramic capacitor, and in particular, alleviates thermal stress between the ceramic laminate and external electrodes and makes cracks less likely to occur in the ceramic due to temperature cycling. And a laminated ceramic capacitor.

[Conventional technology]

A conventional monolithic ceramic capacitor has a structure in which opposing internal electrodes are alternately laminated and embedded via dielectric ceramic sheets, and the internal electrodes are alternately exposed at both ends and then sintered and integrated to form an exposed internal electrode. It is manufactured by attaching an external electrode electrically connected to the end.

And in these capacitors, the expansion coefficient of ceramic is smaller than that of metal. In such a case, in a so-called compression strain type bonded body, thermal stress generated inside the single interface bonded body may cause tensile stress in the outer portion of the ceramic close to the bonded surface to cause cracking.

As a method of mitigating this, for example, as shown in Powder and Powder Metallurgy, Vo136, P.1, February 1989, an intermediate metal layer having a smaller expansion coefficient than that of ceramic is provided between the ceramic and the metal. It is known that the tensile stress generated in the outer portion of the ceramic is relaxed by joining the ceramics with each other.

[Problems to be solved by the invention] In recent years, high-capacity monolithic ceramic capacitor chips have begun to be used in high-frequency power supplies, and they can be tested by a temperature cycle test immediately after or after soldering to the board. An accident has been reported that causes cracks in the ceramic laminate near the electrodes. One of the causes is considered to be a large difference in expansion coefficient between the ceramic laminate, the external electrode, and the solder.

In the conventional monolithic ceramic capacitor, the main component of the ceramic laminate is BaTiO ₃ , and the expansion coefficient is 6 × 10 ^{−6 to} 7 × 10 ⁻⁶ /
℃ (30 ~ 100 ℃), the first layer of the external electrode connected to this is also Ag 19 × 10 ^-6 / ℃, the external electrode has a large expansion coefficient of about 3 times as described above. There is a defect that cracks are easily generated in the ceramic laminate. This is a problem especially in applications where severe temperature cycles are repeated, such as in automobiles.

An object of the present invention is to provide a monolithic ceramic capacitor which can alleviate the stress of expansion and contraction due to temperature cycle and is less likely to cause cracks.

[Means for Solving the Problems]

In the monolithic ceramic capacitor of the present invention, when the expansion coefficient of the ceramic multilayer body is A and the expansion coefficient of the external electrode of the first layer connected thereto is B, B / A1.5 is obtained. It has a characteristic external electrode.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view of an embodiment of the present invention.

As shown in FIG. 1, a first layer external electrode 2 is baked on a ceramic laminated body 1, and a second layer external electrode is formed thereon.
3, and the nth layer external electrode 4 is plated. The expansion coefficient of the first-layer external electrode 2 is 1.5 times or less than the expansion coefficient of the ceramic laminate 1. For example expansion coefficient to the ceramic laminate 1 5.5 × 10 ^-6 /℃(60~150℃),9.9×10 ^-6 /
First, using a Pb-based ceramic laminate at 100 ° C (100-400 ° C)
Etc. with expansion coefficient of 8 × 10 ^-6 / ℃ of Pt alloy descendent foreign electrode 2, Ni plated in the second descendent foreign electrode 3 (13 × 10 ^-6 /
(.Degree. C.), and the solder plated on the n-th layer external electrode 4 is used.

Multilayer ceramic capacitor of the present invention 10μF / 25V, external dimensions
3.2 × 4.5 × 2mm chip with 1.6mm thick glass epoxy PWB
Surface mounted with solder on 100 ° C in the temperature range of -55 to + 125 ° C.
As a result of 0-cycle temperature cycle test, 50 samples
It was found that all of them had no defects such as cracks and could be used in the engine room of a car.

That is, in the conventional monolithic ceramic capacitor, the expansion coefficient A of the external electrode of the first layer is
Although it was much larger than the above, the expansion coefficient of the external electrode of the first layer was made as small as possible, and by making B / A at least 1.5 or less, stress due to temperature cycle can be relieved and cracks are less likely to occur. It turned out to be possible.

[Effect of device]

As described above, according to the present invention, the expansion coefficient of the first-layer external electrode is set to be 1.5 times or less than the expansion coefficient of the ceramic laminated body, so that the stress of expansion and contraction due to the temperature cycle can be relaxed, and the crack is less likely to occur. A ceramic capacitor can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention. 1 ... Ceramic laminate, 2 ... 1st layer external electrode, 3 ...
Second layer external electrode, 4th nth layer external electrode, 5 dielectric ceramic, 6 internal electrode.

Claims (1)

[Scope of utility model registration request] 1. A monolithic ceramic capacitor in which an external electrode is attached to a ceramic laminate, wherein the expansion coefficient of the ceramic laminate is A, and the expansion coefficient of the external electrode of the first layer connected thereto is B. , B / A1.5. A monolithic ceramic capacitor.