JPH10135069A - Formation of external electrode of laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a formation method of an external electrode of a laminated ceramic capacitor by a thin film which ensures connection with an inner electrode. SOLUTION: After a plurality of inner electrodes 2 are arranged inside a body piece 1 formed of ceramic and the inner electrode 2 is exposed from the body piece 1, a metallic film 4 having a diffusion coefficient which is different from that of a material of the inner electrode 2 is formed in an exposed surface of the inner electrode 2 and is subjected to heat treatment. Thereafter, an external electrode 3, consisting of three electrode layers which make a continuity with the inner electrode 2 is provided, and thereby an external electrode of a laminated ceramic capacitor is formed. According to the method, the inner electrode 2 is exposed sufficiently from a side edge face of the body piece 1, connection to the external electrode 3 is ensured, and problems such as loss of electrostatic capacity and increase of dielectric loss tangent (tan δ) can be resolved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming external electrodes of a multilayer ceramic capacitor, and more particularly, to a method for forming external electrodes using a thin film capable of improving the connectivity between an internal electrode and an external electrode.

[0002]

2. Description of the Related Art In general, a multilayer ceramic capacitor having thin-film external electrodes has a hexahedral body piece 1 formed of ceramic as shown in a sectional view of FIG.
A plurality of internal electrodes 2 are alternately arranged in a stacked manner,
Outer electrodes 3 made of a thin film that is electrically connected to the inner electrodes 2 are formed on a pair of side end surfaces of the six side surfaces of the body piece 1 where the inner electrodes 2 are exposed.

The external electrode 3 is formed from this thin film by a sputtering method, a vacuum evaporation method or a plasma spraying method.
After forming the first electrode layer 3a made of Cr having a high adhesion strength to the ceramic body piece 1, a second electrode layer 3b made of Ni serving as a barrier metal for preventing solder erosion is formed on this surface, Further, a third electrode layer 3c made of Ag is formed.

[0004]

In the above-described multilayer ceramic capacitor, it is important to securely connect the internal electrode 2 and the external electrode 3.
After firing the body piece 1 provided with the
Is barrel-polished in order to sufficiently expose the first electrode layer 3a, the second electrode layer 3b, and the third electrode layer 3 on the side end surface of the main body piece 1 by sputtering or the like.
An external electrode 3 having a thickness of c is formed.

However, connection between the internal electrode 2 and the external electrode 3 is caused by insufficient barrel polishing, excessive thinning of the internal electrode 2, chipping at an exposed portion of the internal electrode 2, ceramic coating on the internal electrode 2, and the like. May be insufficient, causing problems such as a loss of capacitance and an increase in dielectric loss tangent (tan δ). SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming an external electrode of a multilayer ceramic capacitor using a thin film, which is reliably connected to an internal electrode in view of the above-mentioned problems.

[0006]

The present invention has the following configuration to achieve the above object. That is, the method for forming the external electrodes of the multilayer ceramic capacitor of the present invention includes:
After arranging a plurality of internal electrodes inside a main body piece made of ceramic and exposing the internal electrodes from the main body piece, a metal film having a diffusion coefficient different from that of the internal electrode material is formed on an exposed surface of the internal electrode. After the heat treatment, an external electrode that is electrically connected to the internal electrode is provided.

In the method of forming an external electrode of a multilayer ceramic capacitor according to the present invention, the diffusion coefficient of the metal film is larger than that of the internal electrode material.
According to the present invention, by forming a metal film having a diffusion coefficient different from that of the internal electrode material and performing a heat treatment, the metal film formed on the side end surface and the internal electrode material disposed inside the ceramic main body piece are formed. In particular, the internal electrode is substantially elongated by this diffusion, and is sufficiently exposed from the side end surface of the main body piece. In particular, the metal film that makes the connection between the internal electrode and the external electrode more secure is provided. Is larger than the internal electrode material, the metal film enters the internal electrode, and as a result,
An alloy of the internal electrode material and the metal film is formed, and the volume of the internal electrode is increased, so that the internal electrode is reliably exposed from the side end surface.

[0008]

Embodiments of the present invention will be specifically described below with reference to the drawings. First, as shown in FIG. 1 (a), on a green sheet 11 in which a dielectric material of titanium oxide, barium titanate, and a Pb-based composite perovskite compound is dispersed in an organic binder, an Ag that becomes an internal electrode when completed is formed. -Conductive paste 12 containing a metal such as Pd or Pd is screen printed, and a predetermined number (about 20 to 100) of the green sheets 11 are stacked and thermocompression bonded. Thereafter, the green sheet 11 that has been thermocompression-bonded is cut along the cutting line 13 to obtain the main body piece 1 of the multilayer ceramic capacitor having a predetermined size.

Then, as shown in FIG. 1B, the main body piece 1 is preliminarily baked and debindered and then fired, and barrel polishing is performed so that the internal electrodes 2 are exposed from a pair of side end surfaces of the main body piece 1. Apply. However, a plurality of (two in this case) internal electrodes 2 may not be sufficiently exposed from the side end surface as surrounded by a circle in the main body piece 1, and in this state, a thin film is formed by a conventional method. If the external electrode is formed on the side end surface of the main body piece 1, the connection between the internal electrode 2 and the external electrode becomes insufficient, which may cause problems such as loss of capacitance and increase in dielectric loss tangent (tan δ).

Therefore, as shown in FIG. 1C, a frame portion 15 having a large number of through holes 14 for accommodating the main body piece 1 is provided.
A jig in which is fixed on the bottom plate 16 is prepared, and the main body piece 1 is inserted into the through hole 14 so that the side end face faces upward. Then, this jig is set in a device capable of forming a metal film on the side end surface, for example, a sputtering device. In the present invention, before forming the external electrode, as shown in FIG. 2D, a metal having a larger diffusion coefficient than the internal electrode 2 made of a metal such as Ag-Pd or Pd, for example, Ag, is formed into a film thickness. 0.1 ~
Sputtering is performed so as to have a thickness of about 1 μm, and metal films 4 are formed on both side end surfaces of the main body piece 1.

Next, the jig is taken out of the main body piece 1 on which the metal film 4 is formed, and is set in a tunnel furnace.
A maximum temperature of 850 ° C. is maintained at 0 ° C./min for 10 minutes, and a heat treatment is performed on the main body piece 1 having the metal film 4 formed on the side end surface. When the heat treatment is performed in this manner, as shown in FIG. 2E, diffusion occurs between the metal film 4 and the internal electrode 2 that is originally exposed and is separated by a small distance due to a difference in diffusion coefficient. The alloy 5 composed of the metal film 4 and the internal electrode 2 is formed in a bridging shape near the side end surface of the main body 1, and the internal electrode 2 is substantially extended and is exposed from the side end surface of the main body piece 1.

On the other hand, on the non-connection end side of the internal electrode 2, the internal electrode 2 and the metal film 4 are spaced at a fixed interval, so that the alloy formation by the above-mentioned diffusion action hardly occurs. In particular, in the present invention, the diffusion coefficient of the Ag metal film 4 is Ag.
Since it is larger than the Pd-based or Pd-based internal electrode 2, the metal film 4 enters the internal electrode 2 side, and the alloy 5 is formed near the side end surface of the main body piece 1.

In this case, assuming that the diffusion coefficient of the internal electrode 2 is larger than the metal film 4, the internal electrode 2 diffuses toward the near end face and the alloy 5 is formed and diffused. However, there is a possibility that a part of the internal electrode 2 is disconnected,
In the present invention, such a problem does not occur because the diffusion coefficient of the metal film 4 is large. In this embodiment, the heat treatment is performed for 85 times.
Although it was performed at a temperature of 0 ° C., it is sufficient that diffusion occurs between the metal film 4 and the internal electrode 2, and the temperature can be appropriately selected from 500 ° C. to 900 ° C.

Next, the main body piece 1 having the alloy 5 formed near the side end face is inserted into a jig similar to that shown in FIG. 1C so that the side end face faces upward to form external electrodes. And a jig, for example, in a sputtering apparatus. And this main body piece 1 is subjected to sputtering,
The external electrodes 3 are formed as shown in FIG. The external electrode 3 is formed by first forming a first electrode layer 3a made of a metal material such as Cr having high adhesion strength to ceramic on one side end surface of the main body piece 1, and then forming the first electrode layer 3a. A second electrode layer 3b made of Ni serving as a barrier metal for preventing solder erosion is formed on the surface, and finally Ag having good solderability is formed.
The third electrode layer 3c made of such a metal material as above is formed. Further, after one external electrode 3 is formed, the jig is turned over so that the other side end face of the main body piece 1 faces upward, and three kinds of electrode materials are sputtered in the same manner as described above, and the first electrode layer 3 is formed.
a, the external electrode 3 including the second electrode layer 3b and the third electrode layer 3c is formed.

As is apparent from FIG.
Is sufficiently exposed from the side end surface by the formation of the alloy 5 with the metal film 4, so that the internal electrode 2 and the external electrode 3 are reliably electrically connected. In the present invention, the third electrode layer 3c is formed of Ag by sputtering, but may be formed by using solder plating.

In the embodiment of the present invention, Ag is used as the internal electrode.
Although Ag is used as the metal film for the Pd-based and Pd-based materials, any metal material may be used as long as the metal film has a diffusion coefficient larger than that of the internal electrode. Here, the diffusion coefficient will be described. The diffusion coefficient of a metal is generally given by the following equation. D = D ₀ exp (−Q / RT) (1) D: Diffusion coefficient (cm ² / sec) D ₀ : Diffusion frequency term (cm ² / sec) Q: Activation energy (kcal / mol) ) R: Gas constant (1.986 cal / K · mol) T: Absolute temperature (K) However, the frequency term D _{0 of} diffusion and the activation energy Q are values specific to metallic materials determined by self-diffusion experiments. .

When the diffusion coefficients of Ag and Pd used in the present invention are calculated, Ag; D ₀ = 0.395 (cm ² / sec), Q = 4
4.09 (kcal / mol), Pd; D ₀ = 0.205 (cm ² / sec), Q
= 63.6 (kcal / mol), and substituting each into equation (1) as T = 1125K gives the diffusion coefficient. Ag is D = 0.38
At 7 (cm ² / sec), Pd was D = 0.199 (cm ² / sec), indicating that the diffusion coefficient of Ag was larger than Pd. Therefore, a metal material can be appropriately selected with reference to the value of the diffusion coefficient calculated by the above equation.

[0018]

As described above, according to the method for forming external electrodes of a multilayer ceramic capacitor according to the present invention,
Diffusion occurs between the internal electrode and the metal film having a different diffusion coefficient and an alloy is formed, so that it is sufficiently exposed from the side end surface of the main body piece, and the connection between the internal electrode and the external electrode is securely performed. Thus, problems such as loss of capacitance and increase in dielectric loss tangent (tan δ) can be solved.

In particular, since the diffusion coefficient of the metal film is larger than that of the internal electrode material, the metal film enters the internal electrode, and a part of the internal electrode is disconnected. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a part of a process of manufacturing a multilayer ceramic capacitor according to the present invention.

FIG. 2 is an explanatory view showing a part of a process of manufacturing the multilayer ceramic capacitor of the present invention.

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

[Explanation of symbols]

 1 body piece 2 internal electrode 3 external electrode 4 metal film 5 alloy part

Claims (2)

[Claims] A plurality of internal electrodes are provided inside a main body piece made of ceramic, and after exposing the internal electrodes from the main body piece, a diffusion coefficient different from that of the internal electrode material is applied to an exposed surface of the internal electrode. A method for forming an external electrode of a multilayer ceramic capacitor, comprising: forming a metal film having a metal film, performing a heat treatment, and then providing an external electrode that is electrically connected to the internal electrode. 2. The method according to claim 1, wherein the diffusion coefficient of the metal film is larger than the material of the internal electrode.