JP3307133B2 - Ceramic electronic components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic electronic component such as a multilayer capacitor, and more particularly to a ceramic electronic component having an improved external electrode structure.

[0002]

2. Description of the Related Art The structure of a multilayer capacitor as an example of a conventional ceramic electronic component will be described with reference to FIG.

The multilayer capacitor 21 includes a ceramic sintered body 22 and external electrodes 24 and 25 formed on both ends of the ceramic sintered body 22. The ceramic sintered body 22 is made of a dielectric ceramic such as barium titanate and has a plurality of internal electrodes 23a to 2
3e is formed. A plurality of internal electrodes 23a to 23e
Are formed so as to overlap with each other via ceramics. Among them, the internal electrodes 23b and 23d are exposed on one end face 22a of the ceramic sintered body 22 and the external electrodes 2b and 23d are exposed.
4 and the internal electrodes 23a, 23c,
23 e is exposed on the other end face 22 b of the ceramic sintered body 22 and is electrically connected to the external electrode 25.

The external electrodes 24 and 25 have a laminated structure composed of four electrode layers. The first electrode layers 24a, 25a which are the lowermost layers of the external electrodes 24, 25 are made of Ag or A
It is composed of a baked layer formed by applying and baking a conductive paste containing a g-Pd alloy.

[0005] Second electrode layers 24b and 25b are formed on the surfaces of the first electrode layers 24a and 25a. The second electrode layers 24b and 25b are each formed of a conductive resin layer formed by applying a silicon-based conductive resin or the like and performing a curing process. The conductive resin layer has lower strength and higher elasticity than other electrode layers. Therefore, as will be described later, an effect of alleviating the stress applied from the outside is exerted. The third electrode layers 24c, 25c formed on the surfaces of the second electrode layers 24b, 25b are composed of a Ni plating layer. This Ni plating layer is formed on the first electrode layer 24.
a, 25a are provided to prevent solder erosion. That is, when the multilayer capacitor 21 is mounted on a printed circuit board or the like, the external electrodes 24 and 25 are soldered.
Is electrically connected to the wiring electrodes on the circuit board. However, the first electrode layers 24a and 25a are formed mainly of a material such as Ag which is liable to be eroded by solder. Therefore, if the Ni plating layer does not exist, the first electrode layer is partially lost due to solder erosion due to soldering during mounting, and the multilayer capacitor 21 cannot function reliably. Therefore, the third electrode layers 24c, 2c
Reference numeral 5c protects the first electrode layers 24a and 25a by plating a material such as Ni which is unlikely to cause solder erosion.

Further, fourth electrode layers 24d, 25d are formed on the surfaces of the third electrode layers 24c, 25c.
The fourth electrode layers 24d and 25d are made of Sn or Sn-Pb
It is composed of a plating layer such as an alloy. A material such as Ni constituting the third electrode layers 24c and 25c has a property that solder erosion hardly occurs, but solderability is not sufficient. Therefore, the solderability of the external electrodes is improved by plating a material having excellent solderability such as Sn.

The multilayer capacitor 21 is used by being mounted on a printed circuit board or the like by soldering. During use, the circuit board receives various physical stresses due to bending of the circuit board and fluctuations in the environmental temperature. The physical stress is applied to the external electrodes 24 and 25 via the soldering layer, affects the external electrodes 24 and 25 and the inside of the ceramic sintered body 22, and may cause a crack or the like. In order to prevent such a situation, in the multilayer capacitor 21, the second capacitor made of a conductive resin layer is used.
The electrode layers 24b and 25b are provided, and deformation of the conductive resin layer and peeling at the interface between the conductive resin layer and the first electrode layers 24a and 25b can be used to reduce external stress. I'm trying.

[0008]

However, in the conventional multilayer capacitor 21, the second electrode layers 24b and 25b and the first electrode layers 24a and 25 made of a conductive resin layer are used.
a, the second electrode layers 24b, 25b
At the interface between the first electrode layer 24a and the first electrode layer 25a progresses over the entire boundary surface, and finally the first electrode layer 2a.
There is a problem that a rupture occurs between the first and second electrode layers 4a and 25a and the second electrode layers 24b and 25b, thereby interrupting conduction of the external electrodes.

An object of the present invention is to provide a highly reliable ceramic electronic component that does not cause external electrode breakage even when a circuit board or a strain due to thermal stress occurs.

[0010]

According to the present invention, there is provided a ceramic electronic component having an external electrode on an outer surface of a ceramic sintered body having an internal electrode, wherein the external electrode has the following configuration.

The external electrode has a first electrode layer formed by first applying and baking a conductive paste to the outer surface of the sintered body. As a material for forming the first electrode layer, various conductive pastes that have been widely used for forming external electrodes of ceramic electronic components can be used. For example, a conductive paste containing a material powder having excellent conductivity, such as Ag, Cu, or an Ag—Pd alloy, as a main component is used. The conductive paste is obtained by kneading glass, a resin binder, and a solvent into the conductive powder as described above. The first electrode layer is formed by applying and baking the above conductive paste on the outer surface of the ceramic sintered body.

[0012] The second electrode layer is partially formed on the surface of the first electrode layer. The second electrode layer is formed of a conductive resin layer having higher elasticity and conductivity than other electrode layers located inside and outside the second electrode layer.

[0013] The third electrode layer is formed in contact with the surface of the second electrode layer and the surface of the first electrode layer. And the fourth
Is formed on the surface of the third electrode layer.

[0014] In the ceramic electronic component according to the limited aspect of the present invention, the second electrode layer is formed in a scattered manner on the surface of the first electrode layer. Furthermore, in the ceramic electronic component according to another aspect of the present invention, the second electrode layer has at least one opening, and the third electrode layer has
It is characterized in that it is formed in contact with the surface of the first electrode layer in the opening of the second electrode layer.

[0015]

In the ceramic electronic component of the present invention, the first electrode layer and the third electrode layer are formed by partially forming the second electrode layer on the surface of the first electrode layer. Are directly joined. The third electrode layer is made of, for example, a metal plating layer of Ni or the like, and has a bonding strength with the first electrode layer made of a baked layer of a conductive paste, which is made of a second layer made of a conductive resin layer. Is larger than the bonding strength between the first electrode layer and the first electrode layer. When stress is applied to the external electrode from the outside, the first
At the interface between the first electrode layer and the second electrode layer, or the stress is reduced by deformation of the conductive resin layer. At the same time, at the joint surface between the first electrode layer and the third electrode layer, by maintaining the joint state against stress,
Ensuring conduction of the entire external electrode.

In the case where the second electrode layer made of a conductive resin is formed on the surface of the first electrode layer, for example, in the form of scattered spots, the size of each island-shaped portion of the conductive resin, or By appropriately setting the arrangement interval, it is possible to achieve harmony between the stress relaxation effect provided by the second electrode layer and the conduction holding effect of the entire external electrode due to the bonding between the first electrode layer and the third electrode layer. it can.

Further, when an opening is provided in the second electrode layer, the stress relieving effect and the effect of ensuring conductivity are achieved in the same manner as described above by appropriately adjusting the opening area of the opening. be able to.

With this configuration, even when an external stress is applied, the stress is reduced by the presence of the second electrode layer, and the bonding state between the first electrode layer and the third electrode layer is reduced. A highly reliable ceramic electronic component can be obtained by securing conductivity by holding.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing embodiments with reference to the drawings. FIG. 1A is a front sectional structural view of a chip type multilayer capacitor according to a first embodiment of the present invention, and FIG. 1B is a side sectional view taken along a cutting line AA. FIG.

Referring to FIGS. 1A and 1B, a multilayer capacitor 1 is formed using a ceramic sintered body 2.
The ceramic sintered body 2 is made of a dielectric ceramic such as barium titanate and has internal electrodes 3a to 3 inside.
f is formed. The internal electrodes 3a to 3f are made of a noble metal material such as Pd or an Ag-Pd alloy, and are arranged so as to overlap with each other via ceramics. Further, the internal electrodes 3a, 3c, 3e are exposed at one end face 2b of the sintered body 2, and the internal electrodes 3b, 3c, 3e are exposed.
d and 3f are exposed on the other end face 2a.

The end faces 2a, 2a of the ceramic sintered body 2
External electrodes 4 and 5 are formed on b. The external electrodes 4 and 5 have a laminated structure of first to fourth electrode layers. The first electrode layers 4a and 5a are made of Ag, Ag-Pd, C
a conductive paste containing a metal powder such as u as a component,
It is formed by baking. The first electrode layers 4 a and 5 a have a thickness of about 10 to 100 μm and are firmly adhered to the end faces 2 a and 2 b of the sintered body 2.

On the surfaces of the first electrode layers 4a and 5a, a second
Electrode layers 4b and 5b are formed. Second electrode layer 4
b, 5b are epoxy-based conductive resins made of the first electrode layer 4;
For example, it is formed by spraying on the surfaces a and 5a with a spray or the like, or by covering with a mesh-shaped mask, applying, and performing a thermosetting treatment. The island-shaped conductive resins 4b and 5b distributed in a scattered manner have a thickness of, for example, about 100 μm and are dispersed at a pitch of about 100 μm. As the conductive resin, other than the epoxy resin, a thermosetting resin such as an acrylic resin, a silicon resin, and a phenol resin may be used. Since these thermosetting resins have higher elasticity than the electrode layer made of other metal materials, they are easily deformed or partially cracked by an external stress, and the action relieves the stress. . Further, since the bonding strength with the first electrode layer is lower than the bonding strength between the other electrode layer and the first electrode layer, separation at the interface with the first electrode layer is also likely to occur. It also exerts a stress relieving effect by its action.

The third electrode layers 4c, 5c are formed so as to cover the surfaces of the first electrode layers 4a, 5a and the second electrode layers 4b, 5b. The third electrode layers 4c and 5c are made of Ni.
It is composed of a plated layer of a metal material that is unlikely to cause solder erosion. Then, the third electrode layers 4c, 5c
Are in direct contact with the surfaces of the first electrode layers 4a and 5a exposed between the second electrode layers 4b and 5b, and are firmly bonded. Therefore, even when stress is applied to the external electrode, the first
The separation between the electrode layer and the third electrode layer hardly occurs, and a good conductive state is maintained.

Further, fourth electrode layers 4d, 5d are formed on the surfaces of the third electrode layers 4c, 5c. The fourth electrode layers 4d and 5d are made of a plating layer of Sn or Sn-Pb alloy. This metal plating layer of Sn or the like has good solderability. Therefore, when mounted on a printed circuit board or the like, the fourth electrode layers 4d and 5d and the electrode wiring on the printed circuit board are firmly joined by soldering.

The multilayer capacitor 1 according to the first embodiment described above
Is when external force is applied to the external electrodes 4 and 5 via the soldering layer due to, for example, bending of the board or expansion or contraction of the board due to a change in ambient temperature in a state of being mounted on a printed circuit board or the like. The second electrode layer 4
The island-shaped conductive resins b and 5b are elastically deformed, or peel off at the interface with the first electrode layers 4a and 5a, thereby reducing stress. Further, as a whole, the external electrodes 4 and 5 include the first electrode layers 4 a and 5 a and the third electrode layers 4 c and 5.
The electrical connection state is maintained by the bonding force of the bonding portion with c. Thereby, the external force can be reduced, and good conductivity can be ensured.

FIG. 2A is a front sectional structural view of a multilayer capacitor according to a second embodiment of the present invention, and FIG.
FIG. 4 is a side cross-sectional structural view from a direction along the cutting line BB.

Referring to FIGS. 2A and 2B, the multilayer capacitor 11 according to the second embodiment includes a second electrode layer 14.
b and 15b are the second electrode layers 4b and 4b according to the first embodiment.
5b, and the other structure is the same as that of the first embodiment. Therefore, here, the structure of the second electrode layers 14b and 15b will be mainly described.

The second electrode layers 14b and 15b are formed of a conductive resin layer formed by applying an epoxy-based conductive resin and then performing a thermosetting treatment. FIG.
As shown in (b), the ceramic sintered body 12 has an opening 16 on the end face. Then, inside the opening 16, the first electrode layers 14a and 15a and the third electrode layers 14c and 15c are directly joined. By providing this bonding portion, the bonding force between the first electrode layer and the third electrode layer is increased. The size of the joint region, that is, the size of the opening 16 of the second electrode layers 14b and 15b depends on the stress relaxation effect of the second electrode layers 14b and 15b and the first electrode layers 14a and 15a and the third electrode layer 14c. , 15c are set to such an extent that the continuity of the conductivity can be ensured by the joining force with the bonding force with the first and second members. For example, the area of this opening is the second electrode layer 1
It is adjusted to about 5 to 50% of the surface area of 4b, 15b.
The opening 16 is not limited to a circular shape.
It may be rectangular or any shape.

Next, specific experimental examples based on the first and second embodiments will be described. In order to verify the characteristics of the multilayer capacitors according to the first and second embodiments, a multilayer capacitor having the following structure was manufactured and tested.

The multilayer capacitor according to the first embodiment (actual
Example 1) Ceramic sintered body: 4.5 × 3.2 × 1.5 mm First electrode layer: A conductive paste containing Ag as a main component is applied so that the thickness after sintering becomes 50 μm, and 800 Fired at a temperature of ° C. Second electrode layer: An epoxy-based conductive resin is applied in a mesh form, heat-cured at a temperature of 150 ° C. for 1 hour, and has a thickness of 1
Formed at 0 μm and 100 μm intervals Third electrode layer: Ni plating layer is formed to a thickness of 6 to 10 μm using barrel plating or the like. Fourth electrode layer: forming a Sn plating layer with a thickness of 3 to 4 μm

[0031]Multilayer capacitor based on a second embodiment
(Example 2) Ceramic sintered body: 4.5 × 3.2 × 1.5 mm ceramic
Mick sintered body First electrode layer: Same as in Example 1 Second electrode layer: Epoxy-based having an opening with a diameter of 1 mm
Apply conductive resin and heat cure at 150 ° C for 1 hour
And a conductive resin layer having a thickness of 50 μm is formed. Third electrode layer: Same as in Example 1. Fourth electrode layer: Same as in Example 1.

For comparison, a multilayer capacitor having the following structure was formed and tested. Comparative Example 1 : A multilayer capacitor having an external electrode structure in which the second electrode layer of Example 1 or Example 2 is omitted. Comparative Example 2 : In contrast to Example 1, a second electrode layer is provided.
Uses a conductive resin layer formed by applying an epoxy-based conductive resin on the entire surface of the ceramic sintered body and subjecting it to a thermosetting treatment at 150 ° C for 1 hour.

Each of the 36 ceramic capacitors of each of the above Examples and Comparative Examples was soldered and mounted on an aluminum substrate, kept at a temperature of -55 ° C. for 0.5 hour, and further kept at a temperature of + 125 ° C. for 0 hour. A heating / cooling temperature cycle test was performed in which the step of holding for 5 hours was one cycle. The results are shown in Table 1 below.

[0034]

[Table 1]

In Table 1, the number of defectives indicates the number of laminated capacitors in which the decrease in the capacitance of the ceramic capacitor became 10% or more after the heating / cooling temperature cycle test was performed.

As can be seen from Table 1, in Comparative Example 1 in which the conductive resin layer was not provided, defective products occurred in 50 cycles, and the defective products had cracks inside the ceramic sintered body. . In Comparative Example 2 in which the conductive resin layer was formed on the entire surface of the first electrode layer, a defect occurred up to 1000 cycles. In this defective product, the first electrode layer and the conductive resin layer Opening failure occurred because the interface was peeled over the entire surface.

On the other hand, in Examples 1 and 2, no failure occurred up to 1000 cycles.
From these results, in the multilayer capacitors according to the first and second embodiments, a multilayer capacitor having higher reliability against external force is obtained as compared with the conventional example.

[Brief description of the drawings]

FIG. 1 is a front cross-sectional structural view of a multilayer capacitor according to a first embodiment of the present invention (a), and a side cross-sectional structural view from a direction along a cutting line AA (b).

FIGS. 2A and 2B are front cross-sectional structural views of a multilayer capacitor according to a second embodiment of the present invention, and side cross-sectional structural views taken along a cutting line BB.

FIG. 3 is a sectional structural view of a conventional multilayer capacitor.

[Explanation of symbols]

1,11 multilayer capacitor 2,12 ceramic sintered body 3a-3f, 13a-13f internal electrode 4,5,14,15 external electrode 4a, 5a, 14a, 15a first electrode layer 4b, 5b , 14b, 15b: second electrode layer (conductive resin layer) 4c, 5c, 14c, 15c: third electrode layer 4d, 5d, 14d, 15d: fourth electrode layer 16: opening

Claims (3)

(57) [Claims] A ceramic sintered body; an internal electrode formed in the ceramic sintered body; and an external electrode formed on an outer surface of the ceramic sintered body. A first electrode layer formed by applying and baking a conductive paste on the surface; and a first electrode layer formed partially on the surface of the first electrode layer and being more elastic than other electrode layers located inside and outside. A second electrode layer made of a conductive resin having a high degree of conductivity and a third electrode layer formed in contact with a surface of the second electrode layer and a surface of the first electrode layer; And a fourth electrode layer formed on the surface of the third electrode layer. 2. The ceramic electronic component according to claim 1, wherein the second electrode layer is formed in a scattered manner on the surface of the first electrode layer. 3. The second electrode layer is partially formed on a surface of the first electrode layer by having at least one opening, and the third electrode layer is formed on the surface of the first electrode layer. 2. The ceramic electronic component according to claim 1, wherein the ceramic electronic component is formed in contact with a surface of the first electrode layer in the opening of the second electrode layer. 3.