JPH08162359A - Chip type ceramic electronic part - Google Patents

Abstract

PURPOSE: To alleviate thermal shock caused by soldering when a mounting operation is conducted and also to alleviate mechanical stress caused by bending a circuit substrate by a method wherein an external electrode is composed of the first porous electrode layer and the second dense electrode layer which covers the whole surface of the above-mentioned first electrode layer. CONSTITUTION: Conductive paste, to be used for formation of the first electrode layer consisting of an alloy composed of a metal component of silver (95wt.%) and paradium (5wt.%), is spread on the end part of a ceramic sintered body 13, and they are fired at 730 deg.C. Then, conductive paste, to be used for formation of the second electrode layer consisting of metal component of silver, is spread on the whole surface of the first electrode layer 15, and a laminated ceramic capacitor, consisting of the first polous electrode layer 15 having the void ratio of 25% and the second dense electrode layer 16 formed on the first electrode layer 15, is obtained. When a heat-resisting test is conducted by dipping the material in the solder bath of 235 deg.C for five seconds, cracks are not generated, and electric characteristics are not impaired even when a part of the porous first electrode layer 15 is collapsed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type ceramic electronic component, and more particularly to the structure of its external electrodes.

[0002]

2. Description of the Related Art For example, as shown in FIG. 2, a monolithic ceramic capacitor, which is a chip-type ceramic electronic component, is
A conductive paste such as an Ag paste is applied to both ends of the ceramic sintered body 1 having a structure in which a plurality of internal electrodes 7 are arranged so as to overlap with each other with a ceramic layer 8 interposed therebetween and are alternately drawn out to both ends. Then, the outer electrode 2 is formed by firing and conducting with the inner electrode.

[0003]

As described above, since the external electrodes 2 of the conventional chip-type ceramic electronic component (multilayer ceramic capacitor) are formed by applying and firing a conductive paste, a dense electrode layer is provided. Has become. Therefore, while the heat of the solder during mounting is easily transmitted to the external electrode 2, a large thermal shock is applied to the ceramic sintered body 1 having poor thermal conductivity. Due to this, as shown in FIG. 4, cracks 9 are formed at the corners of the ceramic sintered body 1, which are the solder-bonded portions, in the vicinity of the external electrodes 2.
May enter. Further, in the conventional chip-type ceramic electronic component (multilayer ceramic capacitor), the external electrode 2 is composed of a dense electrode layer, and the external electrode itself has rigidity. Therefore, as shown in FIG. 3, the external electrodes 2 of the electronic component are mounted and mounted on the electrode lands 4 of the circuit board 3 with the solder 5, and in that state, stress is applied in the direction of the arrow in the figure to cause the circuit board 3 to bend. If so, mechanical stress due to bending of the circuit board 3 directly acts on the ceramic sintered body 1 of the electronic component via the solder 5 and the external electrode 2. As a result,
The same cracks as the cracks 9 caused by the thermal shock of soldering may occur.

Therefore, the present invention provides a chip-type ceramic electronic component capable of relieving thermal shock of soldering during mounting and mechanical stress due to bending of a circuit board and preventing cracks from being generated in a ceramic sintered body. The purpose is to provide.

[0005]

In order to solve the above-mentioned problems, the present invention provides a chip-type ceramic electronic component having an external electrode electrically connected to an internal electrode at an end of a ceramic sintered body. The electrode is a chip-type ceramic electronic component characterized by comprising a porous first electrode layer and a dense second electrode layer covering the entire surface of the first electrode layer.

[0006]

According to the present invention, since the first electrode layer forming the external electrode is formed of the porous layer, its heat capacity can be increased and the propagation of heat and thermal stress can be relaxed. Therefore, the thermal shock at the time of soldering the external electrodes can be mitigated. Moreover, when mechanical stress is applied, a part of the first electrode layer is crushed, and the mechanical stress is relaxed. Therefore, even if the circuit board may be bent after the external electrodes of the ceramic electronic component are soldered to the circuit board, the mechanical stress applied to the ceramic sintered body can be relaxed. Further, by providing the dense second electrode layer so as to cover the entire surface of the first electrode layer, even if a part of the first electrode layer is crushed, the electrical characteristics of the chip-type ceramic electronic component are impaired. In addition, moisture can be prevented from entering the inside of the ceramic sintered body.

[0007]

FIG. 1 is a partial sectional view including an external electrode of a monolithic ceramic capacitor which is a chip-type ceramic electronic component according to an embodiment of the present invention. As shown in FIG. 1, a plurality of internal electrodes 11 are arranged inside the ceramic sintered body 13 so as to overlap with each other via a ceramic layer 12, and are alternately drawn out to the end of the ceramic sintered body 13. An external electrode 14 that is electrically connected to the internal electrode is formed at an end of the ceramic sintered body 13. The external electrode 14 includes a porous first electrode layer 15 having a large number of relatively large voids 17 as shown in FIG. 1 and a dense second electrode layer 15 covering the entire surface of the first electrode layer. It is composed of an electrode layer 16.

When the external electrode 14 of the chip-type ceramic electronic component (multilayer ceramic capacitor) of the present invention is formed by, for example, applying and firing a conductive paste, a porous first electrode is formed at the end of the ceramic sintered body 13. In order to form the first electrode layer 15 and the dense second electrode layer 16 that covers the entire surface of the first electrode layer 15, the conductive paste for forming the first electrode layer is the conductive paste for forming the second electrode layer. Compared to the paste, use one that does not easily sinter at high temperature and can form a porous electrode layer, and use conductive paste for forming the second electrode layer that easily sinters at high temperature and can form a dense electrode layer. Good.

For example, regarding a conductive paste composed of a metal component, a glass component, a resin component, a solvent component, and the like, specifically, the metal component of the conductive paste for forming the first electrode layer is used as an alloy component or the metal component It suffices to add an additive that suppresses sintering. More specifically, when silver is used as the metal component, an alloy with a metal component having a higher melting point than silver can be used. It may be an alloy or a silver / platinum alloy. As the additive that suppresses sintering, for example, oxides such as alumina oxide and silica oxide may be used. When the external electrode 14 is formed by applying a conductive paste and baking, it is necessary to prevent the porous property of the first electrode layer 15 from being damaged by baking the second electrode layer 16. That is, the firing temperature for forming the first electrode layer 15 is preferably the same as or higher than the firing temperature for forming the second external electrode layer 16. When firing the first and second electrode layers 15 and 16 at the same temperature, both electrode layers may be formed by firing once. Further, the metal component of the conductive paste is not limited to one mainly composed of silver, but may be one mainly composed of another metal component such as copper or nickel.

The porosity of the first electrode layer 15 is 15
% To 35% is preferable. The reason is that, when the void area ratio of the electrode layer is less than 15%, the buffer effect of mechanical stress and thermal shock of the porous electrode layer is reduced, and the ceramic sintered body is easily cracked. In addition, the porosity is 35
If it exceeds%, defective conduction with the internal electrode 11 tends to occur. It is more preferable that the porosity is 20% to 30%. Further, even if the second electrode layer 16 is subjected to a moisture resistance test or the surface of the external electrode 14 is subjected to wet electrolytic plating, it is difficult for moisture or a plating solution to enter the inside of the ceramic sintered body, and a highly reliable electronic component is provided. Is formed to such an extent that it can be obtained.

The method of forming the external electrodes of the chip-type ceramic electronic component of the present invention will be described in more detail below.

First, a conductive paste for forming the first electrode layer is applied to the end of the ceramic sintered body 13 shown in FIG.
The metal component of the conductive paste for forming the first electrode layer is silver 9
An alloy consisting of 5% by weight and 5% by weight of palladium is used. Then, the applied conductive paste is fired at 730 ° C. Next, a conductive paste for forming the second electrode layer, the metal component of which is only silver, is applied so as to cover the entire surface of the first electrode layer, and baked at 730 ° C.

The chip-type ceramic electronic component having the external electrodes formed as described above is cut so as to include the external electrodes 14, and the cross-sectional layers of the first and second electrode layers 15 and 16 are scanned with a scanning electron microscope. As a result of measuring the porosity, the porosity of the first electrode layer 15 is 25%, a porous electrode layer is formed, and the second electrode layer is a dense electrode layer (porosity 8% ) Was confirmed to have been formed.

Next, as in this embodiment, the first electrode layer 15 is formed.
A chip-type ceramic electronic component (multilayer ceramic capacitor) in which a porous electrode layer having a porosity of 25% is formed, and a dense second electrode layer 16 is formed on the porous electrode layer, and the external electrode layer 2 shown in the conventional example are dense. Prepare 100 pieces each with only one electrode layer formed, and the external dimension is L dimension 100m
m, W dimension 40 mm, and T dimension 1.6 mm, fixed by an adhesive between the electrode lands formed in the center of the glass epoxy substrate, dipped in a solder bath at 235 ° C. for 5 seconds, and mounted. A heat resistance test was conducted. After that, the external appearance of a portion of the ceramic sintered body 13, 1 which is a solder-bonded portion, which is close to the external electrodes 14, 2 and the portion that is polished, and the cross section thereof is visually observed with a magnifying glass. The presence or absence of cracks in the ceramic sintered body was examined by. The test results are shown in Table 1 below.

[0015]

[Table 1]

From the test results shown in Table 1 above, no cracks were present in all the electronic components according to this example, and the electrical characteristics were not impaired. On the other hand, in the conventional example, 1
There were cracks in 27 out of 00 cracks. Therefore,
It can be seen that the electronic component obtained in this example has excellent heat resistance.

Further, similarly to the above heat resistance test, 100 chip-type ceramic electronic components (multilayer ceramic capacitors) were soldered to the respective substrates, and then stress was applied in the direction of the arrow as shown in FIG. A flexure test was conducted in which the board was flexed by 2 mm. After that, the external electrodes 1 at the corners of the ceramic sintered bodies 13, 1 which are the solder-bonded portions
The presence or absence of cracks in the ceramic sintered body was examined by visually observing the appearance of a portion close to Nos. 4 and 2 and a cross section obtained by polishing the portion with a magnifying glass. The test results are shown in Table 2 below.

[0018]

[Table 2]

From the test results shown in Table 2 above, in this embodiment, all 100 electronic components are free from cracks, and the porous first electrode layer 1 of the external electrode layer 14 is present.
Although 45 crushed parts could be confirmed in part of 5, the electrical characteristics were not impaired. On the other hand, in the conventional example, cracks were present in 50 of 100 electronic components. Therefore, it is understood that the electronic component obtained in this example is excellent in heat resistance and mechanical strength.

The external electrode is not limited to the one formed by applying and firing the conductive paste, but may be formed by vapor deposition or sputtering.

Needless to say, the chip-type ceramic electronic component of the present invention can be applied not only to the monolithic ceramic capacitor but also to any ceramic electronic component having external electrodes such as a chip-type resistor and a chip-type inductor.

[0022]

As described above, according to the present invention, the external electrodes are formed in two layers, and the lower first electrode layer 15 is formed of a porous layer. The mechanical stress applied to the ceramic sintered body 13 due to the thermal shock to the ceramic sintered body 13 and the bending of the substrate at the time of attachment can be relaxed, and the generation of cracks in the ceramic sintered body can be prevented. Further, by providing the dense second electrode layer that covers the entire surface of the first electrode layer, even if a part of the first electrode layer is crushed, the electrical characteristics of the chip-type ceramic electronic component are not impaired. In addition, it is possible to prevent moisture from entering the inside of the ceramic sintered body and prevent deterioration of insulation resistance and the like. Therefore, it is possible to provide a highly reliable chip-type ceramic electronic component as a surface mount component.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a monolithic ceramic capacitor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional monolithic ceramic capacitor.

FIG. 3 is an explanatory view for bending the substrate by applying mechanical stress to the substrate on which the chip-type ceramic electronic component is mounted.

FIG. 4 is an explanatory view showing a state in which a ceramic sintered body has cracks.

[Explanation of symbols]

 13 ... Ceramic sintered body 14 ... External electrode 15 ... First electrode layer 16 ... Second electrode layer 17 ... Void

Claims (1)

[Claims] 1. A chip-type ceramic electronic component having an external electrode electrically connected to an internal electrode at an end of a ceramic sintered body, wherein the external electrode is a porous first electrode layer and the entire surface of the first electrode layer. A chip-type ceramic electronic component characterized by comprising a dense second electrode layer covering the.