JPH07211575A - Ceramic capacitor - Google Patents

Abstract

PURPOSE:To obtain a ceramic capacitor which does not give an inessential stress, in which only a prescribed part can be soldered and connected and which is hard to damage by a method wherein the whole of an external electrode is covered with a first external electrode layer and a second external electrode layer whose solder wettability is high is formed in a part on a side which is soldered and connected when the first external electrode layer is mounted. CONSTITUTION:External electrodes 5 (first external electrode layers 2) which extract internal electrodes collectively are worked at both ends of a ceramic chip part 1 in which dielectric ceramic layers and internal electrode layers have been laminated alternately. The outside of external electrodes 5 is covered with second electrode layers 3 composed of a solder-wettable material. The second external electrode layers 3 use the solder-wettable material such as a silver electrode material or the like which does not contain a glass substance, and they are worked in parts on sides in which a ceramic capacitor on the first external electrode layers 2 is mounted on board. Thereby, the damage of the ceramic capacitor can be reduced when it is soldered to the board or the like, and the reliability of the ceramic capacitor can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic capacitor, and more particularly to the structure of external electrodes such as a multilayer chip capacitor used for surface mounting.

[0002]

2. Description of the Related Art Recently, ceramic capacitors have been widely used as small-sized and large-capacity laminated chip capacitors. In particular, it is often used in surface mount applications, and external electrodes of capacitors are directly connected to a circuit board by soldering. This mounting method is to print solder paste on the substrate, temporarily fix the capacitor on it, reflow method to apply heat to solder, and to pour the melted solder to the entire temporarily fixed capacitor, It is roughly classified into a flow method of soldering the conductor pattern of the substrate and the external electrode of the capacitor. In these surface mounting methods, when the external electrode material of the capacitor is an electrode material with good solder wettability, it is soldered to the entire external electrode part of the capacitor, and the entire external electrode part is soldered to the substrate in the height direction of the capacitor. It will be fixed to. This is because stress concentration occurs near the boundary between the external electrode section of the capacitor and the ceramic chip section due to the mechanical stress applied during the subsequent board assembly and handling, and the thermal stress due to the heat of the temperature cycle. There is a problem that peeling of the electrodes and cracks in the ceramic part frequently occur, resulting in changes in characteristics and failures such as short circuits and interruptions. This problem tends to occur when a relatively large multilayer chip capacitor is mounted by the flow method.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, and by any soldering method, the ceramic chip portion of a capacitor can be soldered only at a predetermined portion that does not give unnecessary stress. Provide a ceramic capacitor having a structure that is difficult to do.

[0004]

In order to solve the above-mentioned problems, the present invention has an improved structure of the external electrodes of the ceramic capacitor so as to limit the parts of the external electrodes that contribute to soldering. In general, the external electrodes of conventional ceramic capacitors are made in a multilayer structure. The inner layer is made of a material that can be reliably connected to the end of the internal electrode of the ceramic chip part, is hard to react with the ceramic, and is firmly fixed to the outside. An external electrode layer is formed using a material that easily wets. It suffices that the external electrode layer on the outside of the external electrode only needs to be wetted by the solder in a portion which is desired to contribute to soldering, and does not contribute to soldering in other portions, and only needs to have good corrosion resistance. In order to achieve the above object, the present invention provides a glass-containing silver electrode, which is a material having excellent corrosion resistance for the first external electrode layer forming the outside of the external electrode portion but having relatively low solder wettability. A silver electrode that does not contain a glass component, which is an electrode material with good wettability with solder, is used as a second external electrode layer in the portion on the entire surface of the external electrode that is desired to contribute to soldering. A ceramic capacitor having an external electrode having a structure in which a layer, a gold electrode layer, a silver-platinum electrode layer or the like is attached and processed on a part of the first external electrode layer is provided.

That is, according to the present invention, a first external electrode made of an electrode material having a low solder wettability is provided in an electrode layer outside an external electrode which covers an end of a ceramic chip portion of a ceramic capacitor and is connected to an internal electrode. The entire surface of the external electrode portion is covered with a layer, and an electrode material having a high solder wettability is formed on a part of the outside of the first external electrode layer that is solder-connected when the first external electrode layer is mounted. And a second external electrode layer provided on the ceramic capacitor, and
In the ceramic capacitor described above, the first external electrode layer is made of silver containing a glass component in a range of 3% to 10%, and the second external electrode layer is made of silver not containing a glass component. A ceramic capacitor having a structure processed into an area less than one half of the external electrode layer area.

[0006]

In the ceramic capacitor of the present invention, the first external electrode layer is hard to react with the solder and the solder is poorly wetted.
For example, when the external electrode is formed by using a silver electrode material containing a glass component in the range of 3% to 10%, when the electrode is baked, a part of the glass component is included in the first external electrode layer shown in FIG. As described above, the glass layer is deposited on the surface to reduce the wettability of the solder. On the other hand, the second external electrode layer is a silver electrode material containing no glass component, and since it is processed only in a part of the first external electrode layer, this second external electrode layer is well compatible with solder, In addition, whichever soldering method is used, soldering can be easily performed between the second external electrode and the conductor of the substrate. Therefore, in the ceramic capacitor of the present invention, since the entire external electrode is not covered with the solder, unnecessary stress is not applied to the external electrode, and the damage of the ceramic capacitor can be prevented without impairing the conductivity of the external electrode. Further, when the second external electrode layer is provided on the surface of the mounting side with an area that is ½ or less of the area of the first external electrode layer, the above effect is most remarkably obtained. Further, regarding the glass-containing silver used for the first external electrode material, the glass component was limited to 3% or more because the wettability of the solder was too good and the ceramic chip portion of the external electrode was less than 3%. This is because the adhesive strength is reduced, and electrode peeling and the like are likely to occur. Further, the reason why the glass component is limited to 10% or less is that conductivity as an external electrode is reduced and electrical connection failure is likely to occur, This is because cracking defects are likely to occur during electrode formation.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the appearance of a multilayer ceramic capacitor according to an embodiment of the present invention, FIG. 2 is a sectional view illustrating an external electrode structure of the multilayer ceramic capacitor shown in FIG. 1, and FIG. 3A and 3B are cross-sectional views showing a state in which the capacitor is soldered to the substrate. FIG. 3A shows a state in which the capacitor is soldered with an appropriate amount of solder, and FIG. 3B shows a state in which the capacitor is soldered with an excessive amount of solder. Show.

As shown in FIG. 1, a monolithic ceramic capacitor used for surface mounting or the like used in the embodiment of the present invention has a ceramic chip portion 1 on which dielectric ceramic layers and internal electrode layers are alternately laminated. The external electrode 5 (in this embodiment, the first external electrode layer 2) is processed so as to collectively pull out the internal electrodes. This first external electrode layer 2 usually needs to be processed so as to adhere firmly to the ceramic chip portion 1 both electrically and mechanically, and silver or the like containing a predetermined amount of glass is used. . This first outer electrode layer, when baked, creates a glassy deposit on the outside. Therefore, as shown in FIG. 2, the external electrode 5 formed by the first external electrode layer 2 has the glass deposition portion 4
Since it covers the surface, it is not compatible with solder and there are many problems in soldering work at the time of mounting in the subsequent process. for that reason,
It is necessary to cover the outside of the external electrode 5 with the second external electrode layer 3 made of a material with which solder is easily wetted. Conventionally, since the second external electrode layer is processed on the entire first external electrode layer 2, as described above, there is a problem that damage is likely to occur after mounting. In the present invention, this second external electrode layer 3
Improved the structure of. As shown in FIGS. 1 and 2, the second external electrode layer 3 is made of a material such as a silver electrode material that does not contain glass and is easily wetted by solder. Is processed on a part of the side mounted on the board.

In an embodiment of the present invention, a glass component-containing silver (Ag) electrode material and a glass component-containing gold (Au) electrode material are used as the first external electrode layer 2, and a glass is used as the second external electrode layer. Silver (Ag) and gold (Au) without ingredients
Samples shown in Table 1 using a silver (Ag) -platinum (Pt) -based electrode material were prepared as a sample of the example and a sample of the comparative example. With respect to these samples, each sample was soldered on a substrate by a flow method, a temperature cycle test of -55 ° C. to 125 ° C. was performed, the occurrence rate of defects due to electrodes was obtained, and the results are shown in Table 1.

[0010]

[Table 1]

As can be seen from Table 1, in sample Nos. 1, 2, 3, 8 and 9 of the examples of the present invention, the incidence of defects is improved. A ceramic capacitor having a first external electrode layer of a silver electrode material having a glass content of 3% or less and a glass content of more than 10% (Sample No. 4 of Comparative Example).
It can be seen that the defect rates of 5 and 5) are high. Sample No. 2,
Comparing Nos. 6 and 7, the second external electrode layer was partially processed as compared with Sample No. 7 in which the second external electrode layer was processed on the entire surface of the first external electrode layer. Sample No.2,6
The defect occurrence rate is improved, and by processing the second external electrode layer in a part of the area of the first external electrode layer,
It can be seen that the occurrence of defects has been improved. Further, when the ceramic capacitor thus obtained is soldered for mounting on a substrate as shown in FIG. 3, even when the amount of solder is appropriate in FIG. Even in the case of FIG. 3B in the state where the amount is excessive, the solder does not adhere to the entire external electrode 5, and the solder adheres to only the second external electrode layer 3 to be soldered, which is unnecessary. Prevents stress from being applied to the ceramic capacitor.

[0012]

As described above, according to the present invention,
It is possible to provide a ceramic capacitor with improved reliability by reducing damage to the ceramic capacitor when soldered to a substrate or the like.

[Brief description of drawings]

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

FIG. 2 is a sectional view illustrating an external electrode structure of the multilayer ceramic capacitor shown in FIG.

FIG. 3 is a cross-sectional view showing a state in which a ceramic capacitor according to the present invention is soldered to a substrate, FIG. 3 (a) is a diagram showing a state of being soldered with an appropriate amount of solder, and FIG. 3 (b) is an excess. The figure which shows the state soldered by the amount of solder.

[Explanation of symbols]

 1 Ceramic Chip Part 2 First External Electrode Layer 3 Second External Electrode Layer 4 Glass Precipitating Part 5 External Electrode 6 Solder 7 Substrate

Claims (2)

[Claims] 1. A first external electrode layer made of an electrode material having low wettability of solder in an electrode layer outside an external electrode which covers an end of a ceramic chip portion of a ceramic capacitor and is connected to an internal electrode. The entire outer surface of the first external electrode layer and a part of the side to which solder connection is made when the first external electrode layer is mounted outside the first external electrode layer. A ceramic capacitor having an external electrode layer. 2. The ceramic capacitor according to claim 1, wherein the first external electrode layer contains 3% to 1% of a glass component.
The second external electrode layer is made of silver contained in an amount of 0%, and the second external electrode layer is made of silver not containing a glass component, and is characterized by being processed into an area that is ½ or less of the area of the first external electrode layer. Ceramic capacitor.