JPH11162771A - Laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a capacitor body from being cracked and external electrodes from peeling off. SOLUTION: A laminated ceramic capacitor has external electrodes 5a and 6a formed at the both ends of a capacitor body 2 wherein internal electrodes 3 and 4 are arranged via ceramic layers, and the external electrodes 5a and 6a are configured by forming electrode layers 11 formed by sequentially laminating a conductive paste of Ag or Ag alloy by dipping and baking it, conductive epoxy thermosetting resin layers 12, nickel plating layers 13, and tin group layers 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor having improved external electrodes.

[0002]

2. Description of the Related Art FIG.
This will be described below. FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor 1, which is composed of a capacitor body 2 of a ceramic sintered body made of a dielectric material such as barium titanate. Inside the capacitor body 2, a ceramic layer (dielectric layer) is provided. , Internal electrodes 3 and 4 made of a noble metal material such as Ag or an Ag-Pd alloy or a base metal material such as nickel (Ni) are provided. The internal electrode 3 is electrically connected to the external electrode 5, and the internal electrode 4 is electrically connected to the external electrode 6.

The external electrodes 5 and 6 are each composed of an electrode layer having a three-layer structure. That is, there is an electrode layer 7 formed by applying and baking a conductive paste made of Ag or an Ag-Pd alloy on the surface of the capacitor body 2, and the surface of the electrode layer 7 is unlikely to suffer from solder erosion. A nickel plating layer 8 made of a material is formed, and tin (Sn) or solder (Sn) is formed on the nickel plating layer 8.
-Pb alloy).

Another technique is disclosed in Japanese Patent Publication No. 58-40161.
And Japanese Patent Application Laid-Open No. 4-257111.

According to the former technique, a conductive layer made of a conductive paste is provided on an end portion of an insulating substrate or on both sides of a circuit element, and a conductive layer is formed on the conductive layer via an Ag-resin-based conductive resin layer. In this configuration, the conductive resin layer enhances the adhesive strength to the outer conductive layer, thereby increasing the number of times parts can be replaced.

In the latter Japanese Patent Application Laid-Open No. Hei 4-257221, a lead-out electrode is provided outside the chip-type electronic component body and is electrically connected to the internal electrode, and a buffer made of an epoxy / phenol-based thermosetting resin is provided on the lead-out electrode. This is a horizontal structure in which the material layer is covered and a plating layer is further provided, thereby absorbing external mechanical and thermal stress.

[0007]

However, according to the monolithic ceramic capacitor 1 of FIG. 3, since the electrode layer 7 is formed by baking, the joints between the external electrodes 5, 6 and the capacitor body 2, especially the external electrodes Stresses are generated in the peripheral portions of 5 and 6 due to the sintering shrinkage of the metal powder and the diffusion of the glass component into the dielectric layer. Therefore, when the multilayer ceramic capacitor 1 is mounted on a circuit board, a temperature cycle test or a thermal cycle test is performed. Under a sudden thermal change such as an impact test, or under such a severe environment, the stress absorption due to the difference in thermal expansion coefficient between the dielectric layer, the external electrodes 5, 6, the solder, and the circuit board. Insufficiently, cracks occur in the capacitor body 2 from residual stress portions around the external electrodes 5 and 6, and as a result, the multilayer ceramic capacitor 1 functions. Kuna' which was.

On the other hand, in each of the techniques in which a conductive resin layer is formed as disclosed in Japanese Patent Publication No. 58-40161 and Japanese Patent Application Laid-Open No. 4-257111, a stress directed outward from a main body is applied to an external electrode. In this case, the conductive resin layer is likely to be partially peeled off, so that the fixing force with the mounting substrate is reduced, and the chip itself has fallen off.

Accordingly, the present invention has been completed in view of the above circumstances, and its purpose is to prevent cracks from occurring in the capacitor body even when stress is generated in an extreme temperature environment such as a cooling / heating cycle. An object of the present invention is to provide a high-quality and highly reliable multilayer ceramic capacitor in which external electrodes do not peel off.

[0010]

A multilayer ceramic capacitor according to the present invention forms a capacitor body by alternately laminating a first internal electrode group and a second internal electrode group via a dielectric layer. The end of the first internal electrode group is exposed on one end surface of the capacitor body, the end of the second internal electrode group is exposed on the other end surface, and external electrodes are formed on both end surfaces, respectively. A baked electrode layer;
It is characterized in that a conductive epoxy thermosetting resin layer containing metal powder, a nickel plating layer, and a tin or solder plating layer are sequentially laminated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a multilayer ceramic capacitor according to the present invention will be described in detail with reference to FIGS. FIG. 1 shows a sectional structure of a multilayer ceramic capacitor 10 of the present invention, and FIG.
Shows a cross-sectional structure of another multilayer ceramic capacitor 10a of the present invention. In these figures, the same portions as those of the conventional multilayer ceramic capacitor 1 are denoted by the same reference numerals.

In the multilayer ceramic capacitor 10 shown in FIG. 1, the first ceramic body is interposed in a capacitor body 2 made of a dielectric such as barium titanate.
As the internal electrode group and the second internal electrode group, the P
internal electrodes 3 and 4 made of a noble metal material such as d or Ag-Pd alloy or a base metal material such as nickel (Ni).
Is arranged.

To manufacture the capacitor body 2 having the above-described structure, a paste of metal powder to be used as an internal electrode is printed on a predetermined area of the ceramic green sheet so that a large number of rectangles are regularly arranged. Are laminated and cut into dimensions in the laminating direction to form a chip material, and then the chip material is fired at a predetermined atmosphere and temperature to produce a chip material.

Next, external electrodes 5a and 6a are formed on both end surfaces of the capacitor body 2 having the above configuration. Capacitor body 2
A conductive paste made of Ag or an Ag alloy is dipped and applied to the surface of the substrate. Then, the applied conductive paste is baked in a predetermined atmosphere and temperature to form the electrode layer 11 as the baked electrode layer. Then, a conductive epoxy-based thermosetting resin layer 12 is formed on the surface of the electrode layer 11, a nickel plating layer 13 made of a material that is unlikely to be eroded by solder is formed thereon by electrolytic plating or the like, and furthermore, tin ( A tin or solder plating layer 14 (hereinafter abbreviated as a tin-based layer) made of a material such as Sn) or solder (Sn—Pb alloy) is formed.

The epoxy-based thermosetting resin layer 12 is formed by sequentially applying, drying, and curing a conductive resin paste of an epoxy-based thermosetting resin.

The conductive resin paste is a mixed composition of a metal powder, an epoxy resin binder, and a curing agent, or a mixed composition in which an organic medium is added, wherein the metal powder and the thermosetting resin component are mixed. It is blended in a weight ratio of 100: 5 to 100: 45.

As the metal powder, gold, silver, platinum, palladium, rhodium, nickel and copper are used alone or in combination.

The epoxy resin binder comprises a compound having two or more epoxy groups in a molecule,
It cures under the action of a curing agent or catalyst. The epoxy resin is selected from a liquid epoxy resin such as a bisphenol A epoxy resin, a bisphenol F epoxy resin, and a bisphenol AD epoxy resin.

As the curing agent, a polyamid curing agent, an aliphatic polyamine curing agent, a cycloaliphatic polyamine curing agent, an aromatic polyamine curing agent, dicyandiamide and the like are used.

As the organic medium, ethanol, i, n
-Aliphatic alcohols such as propanol, butanol,
Alternatively, there are esters of these alcohols such as acetate, propionate and the like. Further, methyl carbitol, ethyl carbitol, butyl carbitol,
Carbitol solvents such as butyl carbitol acetate, acetone, methyl ethyl ketone, 2-pentanone,
Ketone solvents such as 3-pentanone and cyclohexanone, benzene, toluene, xylene, ethylbenzene,
Examples include hydrocarbon solvents such as turpentine, cyclohexane, methylcyclohexane, and methylpentane.

The conductive resin paste is applied and adhered by a conventionally known means, for example, screen printing, dipping or the like. Next, the paste is temporarily dried at a temperature of 80 to 140 ° C., and thereafter, at a temperature of 60 to 120 ° C. for 15 to 9 to completely remove a solvent component in the paste.
Remove solvent for 0 minutes. After a while, 150-250
The resin is cured by heating at a temperature of 30 ° C. for 30 to 120 minutes to form a conductive epoxy-based thermosetting resin layer.

Thus, according to the multilayer ceramic capacitor 10 of the present invention, when the conductive epoxy-based thermosetting resin layer 12 as described above is provided, the epoxy-based resin in the layer 12 is crosslinked by the reaction with the curing agent. The cured resin has a three-dimensional network structure and a low molecular weight epoxy resin is used, so that the crosslink density can be further improved. The system thermosetting resin layer 12 absorbs stress,
It can absorb stress against external force directed outward from the main body,
As a result, cracks did not occur in the capacitor body 2, and peeling of the external electrodes 5a and 6a did not occur.

FIG. 2 shows another multilayer ceramic capacitor 10.
According to a, the external electrodes 5a,
In the case where 6a is covered, a part thereof extends to the end on the main surface of the capacitor body 2. In the figure, both external electrodes 5
The direction connecting between a and 6a is defined as the X direction. With respect to the X direction, the direction parallel to the end face of the capacitor body 2 and the thickness direction of the capacitor body 2 and perpendicular to the X direction is defined as the Y direction. The plane direction of the electrodes 3, 4 and the direction perpendicular to the X direction is defined as the Z direction.

And an end of the extended electrode layer 11;
The distance Q in the X direction from the point of maximum thickness on the end face of the capacitor body 2 is Q, and the distance Q / P is 0.25-0. 8, preferably from 0.45 to 0.6 is preferable in the following points.

That is, even in an environment of an extreme temperature change or a temperature cycle, by setting as described above, the stress generated at the end of the electrode layer 11 due to the baking of the electrode layer 11 can be reduced. Stress can be absorbed by the layer 12, whereby cracks do not occur in the capacitor body 2 and the external electrodes 5a and 6a do not peel off.

[0026]

(Example 1) In a multilayer ceramic capacitor 10 of the present invention, a conductive paste containing Ag as a main material and containing a glass frit is applied in a thickness of 5 to 20 μm, and dried.
The electrode layer 11 is formed by baking. Next, a conductive resin paste in which an Ag-based filler is dispersed in an epoxy-based resin is applied to a thickness of 20 to 200 μm so as to completely cover the electrode layer 11, dried, and then desolvated at a temperature of 80 to 120 ° C. Then, it is cured at a temperature of 150 to 200 ° C., whereby the epoxy-based thermosetting resin layer 12 is formed. Subsequently, a nickel plating layer 13 is formed by electrolytic plating, and a tin-based layer 1 is formed on the nickel plating layer 13.
No. 4 was formed by electrolytic plating, and was made into a 2012 type having a total length of 2.0 mm according to the standard.

In producing such a laminated ceramic capacitor, an epoxy-based thermosetting resin layer 12 as in the present invention and various layers as comparative examples were formed. 1 to 10. However, the sample No. 7
The epoxy-based thermosetting resin layers used in Sample Nos. To 9 of the present invention are the same as those of Sample Nos. The molecular weight is larger than those of Sample Nos. 7 <Sample No. 8 <Sample No. In the order of 9, they are even larger.

[0028]

[Table 1]

A temperature cycle durability test and a high temperature load test were performed on these 10 types of samples.

In the temperature cycle durability test, the battery was kept in an atmosphere at -55 ° C. for 30 minutes, and then kept in an atmosphere at 150 ° C. for 30 minutes, and the cooling / heating cycle was repeated 1,000 times to reduce the capacity, and The initial fixing strength and the fixing strength after the test were examined. At that time, using 50 samples, the frequency of occurrence of cracks and the frequency of peeling of the external electrodes were determined in a ratio. As shown in the table, this ratio is represented by the number of numerators obtained by denominating 50 pieces.

For the high temperature load test (DC × 2),
Place 50 samples in an atmosphere of 125 ° C.
The deterioration status up to 0 hours was examined, and the reliability was classified into three stages. The mark “○” indicates that no deterioration has occurred even after 1000 hours, the mark “△” indicates that the film has deteriorated after approximately 750 hours, and the mark “X” indicates that the film has deteriorated after approximately 500 hours.

As is clear from the table, the sample N of the present invention
o. 1 and Sample No. Regarding 2, the initial bond strength was high, and even if a temperature cycle durability test was performed,
Almost no drop. In addition, no cracks occurred in the capacitor body, and the external electrodes were peeled off. Moreover, even in the high-temperature load test, no deterioration occurred even after 1000 hours.

On the other hand, the sample No. In Nos. 3 to 10, both the temperature cycle durability test and the high-temperature load test were inferior. In particular, the sample No. In No. 9, it dropped off from the mounting board.

Example 2 The multilayer ceramic capacitor sample No. of Example 1 was used. In the preparation of Sample No. 1, the interval Q between the electrode layers 11 and the interval P between the epoxy-based thermosetting resin layers 12 and the ratio Q / P were changed respectively, and the above-mentioned temperature cycle durability test, high-temperature load test, and adhesion strength were further changed. Was measured, the results as shown in Table 2 were obtained. Note that ten samples were prepared for each of the adhesion strengths, and a tensile test in the terminal L direction was performed.

[0035]

[Table 2]

Sample No. 12 to sample no. With regard to No. 15, good results were obtained in the adhesion strength test, the temperature cycle durability test, and the high-temperature load test.
On the other hand, the sample No. Reference numeral 11 indicates that the electrode layer 11 was formed only on the end face of the capacitor body 2, so that the adhesion strength was the smallest, and both were judged to be defective due to thermal stress in the temperature cycle durability test and the high-temperature load test.
In addition, the sample No. In Nos. 16 and 17, the gap Q between the electrode layers 11 was large, so that stress was applied due to tightening caused by baking, and cracks occurred in the capacitor body 2 due to temperature cycling, resulting in a reduction in capacity.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements may be made without departing from the scope of the present invention.

[0038]

As described above, according to the multilayer ceramic capacitor of the present invention, a conductive paste containing a metal powder is provided between an electrode layer coated with a conductive paste and baked on an external electrode and a nickel plating layer. Since the epoxy-based thermosetting resin layer was formed, it was mounted on a circuit board, and even if stress was generated due to temperature cycling or thermal shock, cracks did not occur in the capacitor body, and the external electrodes did not peel off, Moreover, the bonding strength with the mounting substrate is excellent, and as a result, a high-quality and long-term reliable multilayer ceramic capacitor can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a multilayer ceramic capacitor according to the present invention.

FIG. 2 is a cutaway view of another multilayer ceramic capacitor of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 10, 10a Multilayer ceramic capacitor 2 Capacitor body 3, 4 Internal electrode 5, 6, 5a, 6a External electrode 7, 11 Electrode layer 8, 13 Nickel plating layer 12 Epoxy-based thermosetting resin layer 14 Tin-based layer

Claims (1)

[Claims] 1. A capacitor body is formed by alternately laminating a first internal electrode group and a second internal electrode group via a dielectric layer, respectively, and an end of the first internal electrode group is connected to the capacitor body. On the other hand, the end of the second internal electrode group is exposed to the other end face on one end face, and an external electrode is formed on each end face. The external electrode is a baked electrode layer and a conductive powder containing metal powder. A multilayer ceramic capacitor comprising: a laminated epoxy thermosetting resin layer; a nickel plating layer; and a tin or solder plating layer.