WO2005055257A1

WO2005055257A1 - Conductive paste and laminated ceramic electronic component

Info

Publication number: WO2005055257A1
Application number: PCT/JP2004/017060
Authority: WO
Inventors: Seiji Koga; Kiyotaka Maegawa; Kunihiko Hamada
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2003-12-01
Filing date: 2004-11-17
Publication date: 2005-06-16
Also published as: JPWO2005055257A1; JP4211783B2

Abstract

A conductive paste that can be advantageously used in the formation of external electrode (5) composed mainly of copper on an external surface of laminate (4) furnished with internal conductor films (3) composed mainly of nickel, which conductive paste can avoid cracking of the laminate (4) attributed to thickening of the internal conductor films (3) caused by excess diffusion of copper contained in the external electrode (5) into the internal conductor films (3). There is provided a conductive paste comprising copper powder, iron oxide powder, glass powder and an organic vehicle, wherein iron oxide powder is contained in an amount of 3 to 40 vol.% based on the total volume of copper powder and iron oxide powder, and glass powder in an amount of 10 to 25 vol.% based on the total volume of copper powder, iron oxide powder and glass powder.

Description

Specification

Conductive paste and multilayer ceramic electronic components

Technical field

The present invention relates to a conductive paste and a multilayer ceramic electronic component, and in particular, to a conductive base suitably used for forming external electrodes of the multilayer ceramic electronic component, and a method using the conductive paste. The present invention relates to a multilayer ceramic electronic component having external electrodes formed thereon.

Background art

A general structure of a multilayer ceramic capacitor as an example of a multilayer ceramic electronic component that is of interest to the present invention is shown in a cross-sectional view in FIG.

As shown in FIG. 1, a multilayer ceramic capacitor 1 includes a plurality of stacked ceramic layers 2 and a plurality of internal conductor films 3 formed along an interface between the ceramic layers 2. It has the body 4 and has two external electrodes 5 formed on the outer surface of the laminate 4 and on each end of the laminate 4.

The internal conductor film 3 is formed so that a part of each edge reaches the outer surface of the multilayer body 4 and is electrically connected to the external electrode 5. The internal conductor films 3 electrically connected to each other and the internal conductor films 3 electrically connected to the other external electrode 5 are alternately arranged in the laminating direction.

[0005] Further, on the external electrodes 5, for the purpose of improving solder wettability, heat resistance, and the like, for example,

Then, a first plating film 6 made of nickel is formed, and a second plating film 7 made of tin or solder is further formed thereon.

In such a multilayer ceramic capacitor 1, usually, the external electrode 5 is formed by applying a conductive paste containing a conductive metal powder, a glass powder, and an organic vehicle to each end of the multilayer body 4. , Formed by baking this.

[0007] By the way, recently, as a conductive component contained in the internal conductor film 3, a base metal, particularly, nickel has been increasingly used. As described above, when the internal conductor film 3 is mainly composed of nickel, the conductive paste contained in the conductive paste used to form the external electrode 5 is used. It is preferable to use copper powder as the conductive metal powder (for example, see Patent Documents 1 and 2). This is because when the conductive paste is baked to form the external electrode 5, solid phase diffusion occurs between nickel contained in the internal conductor film 3 and copper contained in the conductive paste for the external electrode 5. This is because a Ni—Cu alloy can be generated to ensure a good bonding state between the internal conductor film 3 and the external electrode 5.

[0008] As described above, while the conductive paste for forming the external electrode 5 contains copper, the conductive paste for forming the internal conductor film 3 contains nickel, as described above. Here, when a conductive paste is baked to form the external electrode 5, copper contained in the external electrode 5 may excessively diffuse into nickel contained in the internal conductor film 3.

[0009] Such excessive diffusion of copper causes the internal conductor film 3 to be thickened, and causes cracks in the laminate 4 due to the stress generated at that time. The cracks generated in the multilayer body 4 reduce the reliability of the multilayer ceramic capacitor 1.

[0010] In order to prevent excessive diffusion of copper contained in the external electrode 5 into the internal conductor film 3 as described above, it is conceivable to lower the baking temperature of a conductive paste for forming the external electrode 5. You.

[0011] If the conductive paste is baked at a low temperature while pressing, the denseness of the external electrode 5 may not be sufficiently secured. Therefore, in the above-described plating step for forming the plating films 6 and 7, the plating solution passes through the open pores existing in the external electrode 5 or dissolves the glass component contained in the external electrode 5, It may penetrate into the laminate 4 and reduce the electrical insulation of the ceramic layer 2.

[0012] In order to increase the denseness of the external electrode 5, a force that is required to be baked at a higher temperature is obtained. The fluidity of the glass component contained in the external electrode 5 increases by force, which causes a problem caused by excessive diffusion into the conductive film 3, and the glass component emerges on the surface of the external electrode 5 and plating occurs. In the plating process for forming the films 6 and 7, plating failure may be caused.

Patent Document 1: JP-A-59-184511

Patent Document 2: JP-A-11-97281 Disclosure of the invention

Problems to be solved by the invention

Therefore, an object of the present invention is to provide a conductive paste and a multilayer ceramic electronic component having an external electrode formed using the conductive paste, which can solve the above-described problems.

Means for solving the problem

The present invention is first directed to a conductive paste used to form external electrodes of a multilayer ceramic electronic component. The conductive paste according to the present invention contains copper powder, glass powder, and an organic vehicle, but is characterized by further containing iron oxide powder in order to solve the above-mentioned technical problem. The iron oxide powder contains 3 to 40% by volume based on the total volume of the copper powder and the iron oxide powder, and the glass powder contains the total volume of the copper powder, the iron oxide powder and the glass powder. , 10-25% by volume.

[0015] The present invention also provides a laminated body formed of a plurality of laminated ceramic layers and an internal conductor film containing nickel as a main component and formed along the interface between the ceramic layers, The present invention is also directed to a multilayer ceramic electronic component including an external electrode containing copper as a main component and formed on the outer surface of the laminate so as to be electrically connected to the conductor film.

[0016] The multilayer ceramic electronic component according to the present invention is characterized in that the external electrode is a sintered body obtained by sintering the above-described conductive paste according to the present invention.

[0017] The present invention also provides a plurality of stacked ceramic layers mainly composed of a composite oxide containing titanium, and an internal conductor mainly composed of nickel formed along an interface between the ceramic layers. A multilayer ceramic electronic component comprising: a multilayer body constituted by a film; and an external electrode mainly composed of copper formed on an outer surface of the multilayer body so as to be electrically connected to the internal conductor film. Also directed to.

[0018] In the multilayer ceramic electronic component, according to the present invention, the external electrode includes, as a glass component, zinc borosilicate glass containing iron oxide and titanium oxide, and a ceramic layer and an external electrode in contact with the ceramic layer. Contains nickel, zinc, titanium and iron at the interface with the electrode This is characterized in that a reaction layer is formed by forming a spinel-structured crystalline phase.

The invention's effect

[0019] The conductive paste according to the present invention contains a predetermined amount of iron oxide powder as described above. The inclusion of iron oxide has the following effects when the conductive paste is used for forming external electrodes of a multilayer ceramic electronic component.

First, iron oxide contained in the conductive paste has an oxygen donating effect, and is reduced during baking to release oxygen. The released oxygen accelerates the degreasing of the conductive paste, improves the sinterability of the copper powder contained in the conductive paste, and as a result, improves the denseness of the external electrode.

[0021] Further, at the time of baking of the conductive paste, the oxidized iron is dissolved in the glass component contained in the conductive paste, and the glass component in which the oxidized iron is dissolved is provided in the laminate. The ceramic constituting the ceramic layer reacts, and a reaction layer is formed at the interface between the ceramic layer and an external electrode in contact with the ceramic layer.

[0022] The reaction layer first prevents the components of the external electrode from excessively diffusing into the internal conductor film. As a result, the copper contained in the external electrode becomes excessively contained in the internal conductor film, for example, nickel. This prevents the internal conductor film from becoming thicker, and can cause cracks in the laminate to increase the thickness.

Further, the presence of the reaction layer effectively prevents the plating solution from entering the laminate. The above-described improvement in the fineness of the external electrodes also contributes to prevention of intrusion of the plating solution. Further, as described above, the glass component in the conductive paste dissolves the iron oxide therein, thereby improving the plating solution solubility. This improvement in the solubility of the glass component in the plating solution also contributes to preventing the penetration of the plating solution.

From the above, according to the present invention, it is possible to provide a multilayer ceramic electronic component having excellent reliability such as electrical insulation and weather resistance.

Brief Description of Drawings

FIG. 1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 as an example of a multilayer ceramic electronic component that is of interest to the present invention. [FIG. 2] FIG. 2 is an enlarged cross-sectional view schematically illustrating a portion A of the multilayer ceramic capacitor 1 shown in FIG. 1, and shows external electrodes 5 formed using a conductive paste according to the present invention. 3 illustrates a reaction layer 8 formed at the interface between the ceramic layer 2 and the ceramic layer 2.

Explanation of symbols

[0026] 1 Multilayer ceramic capacitor

2 Ceramic layer

3 Internal conductor film

4 laminate

5 External electrode

6, 7 Plating film

8 Reaction layer

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] The conductive paste according to the present invention is used for forming external electrodes of a multilayer ceramic electronic component. Hereinafter, a case where the conductive paste according to the present invention is applied to the multilayer ceramic capacitor 1 will be described with reference to FIG. 1 again. The description of the basic configuration of the multilayer ceramic capacitor 1 is referred to the above description.

[0028] In the multilayer ceramic capacitor 1, the external electrode 5 is formed from a sintered body obtained by applying the conductive paste according to the present invention on the outer surface of the multilayer body 4, drying, and firing. Be composed.

[0029] The conductive paste contains iron oxide powder in addition to copper powder, glass powder, and an organic vehicle. Here, the copper powder is copper or a metal having copper as a main component. The iron oxide powder is composed of iron oxide of any of FeO, FeO and FeO.

2 3 3 4

May be. Further, as the glass powder, for example, a powder having a zinc borosilicate-based glass power is preferably used.

[0030] The iron oxide powder in the conductive paste according to the present invention is contained in an amount of 3 to 40% by volume based on the total volume of the copper powder and the iron oxide powder. The glass powder should be contained in an amount of 10 to 25% by volume based on the total volume of the copper powder, the iron oxide powder, and the glass powder. It is.

FIG. 2 is a cross-sectional view schematically showing an enlarged part A of the multilayer ceramic capacitor 1 shown in FIG.

As shown in FIG. 2, when the external electrode 5 is formed using the conductive paste according to the present invention, the interface between the ceramic layer 2 included in the laminate 4 and the external electrode 5 in contact with the ceramic layer 2 includes: A reaction layer 8 is formed.

[0033] As the ceramic constituting the ceramic layer 2, for example, titanium such as BaTiO is contained.

Three

In the conductive paste used for forming the external electrodes 5, the inner conductor film 3 is mainly composed of nickel, and in the conductive paste used for forming the external electrodes 5, zinc borate-based glass powder is used as the glass powder. When such a material is used, the external electrode 5 is in a state of containing zinc borosilicate glass containing iron oxide and titanium oxide as a glass component, and nickel and zinc are contained in the reaction layer 8. It has been confirmed that a crystalline phase having a spinel structure containing titanium and iron is formed.

[0034] As described above, the content of the iron oxide powder in the conductive paste is limited to 3 to 40% by volume based on the total volume of the copper powder and the iron oxide powder, for the following reason. by.

[0035] That is, when the content of the iron oxide powder is less than 3% by volume, the effect of the iron oxide powder content is not sufficiently exhibited. Therefore, degreasing of the conductive paste, which has a small oxygen donating effect by iron oxide, cannot be sufficiently promoted, and the denseness of the external electrode 5 cannot be sufficiently improved. In addition, a reaction layer due to the reaction between the glass component in the external electrode 5 and the ceramic is hardly generated at the interface between the ceramic layer 2 and the external electrode 5 in contact with the ceramic layer 2, and the copper internal conductor film contained in the external electrode 5 Excessive diffusion into 3 cannot be suppressed, and cracks tend to occur in laminate 4.

[0036] On the other hand, when the content of the iron oxide powder exceeds 40% by volume, sintering of the copper powder in the conductive paste is suppressed, and the obtained external electrode 5 becomes porous, and the laminated ceramics The reliability of the capacitor 1 decreases.

[0037] Further, as described above, the content of the glass powder in the conductive paste is limited to 10 to 25% by volume with respect to the total volume of the copper powder, the oxidized iron powder and the glass powder. If the volume is less than 10% by volume, the voids are sufficiently filled with the glass component in the external electrode 5. This is because the external electrode 5 is in a porous state because it cannot be formed, and when the content exceeds 25% by volume, a relatively large amount of glass component precipitates on the surface of the external electrode 5, which may lead to poor plating.

[0038] In order to promote degreasing during baking of the conductive paste, the oxygen concentration of the atmosphere during baking should be increased instead of relying on the oxygen donating effect of the oxidized iron powder contained in the conductive paste. Although it is conceivable that degreasing of the surface layer of the external electrode 5 may be promoted even when the oxygen concentration in the atmosphere is increased in this way, it is desirable to sufficiently promote degreasing inside the external electrode 5. I can't.

[0039] Instead of including iron oxide powder in the conductive paste, it is also conceivable to include iron oxide in a glass component contained in the conductive paste. However, iron oxide in the glass component is less likely to be reduced in the baking process than iron oxide contained as a powder in the conductive paste, and thus has a lower oxygen donating effect.

Further, instead of iron oxide, a metal oxide having a relatively high equilibrium oxygen partial pressure (a metal oxide that is easily reduced) such as a metal oxide such as cobalt oxide or nickel oxide is used. Although it is conceivable that these cobalt oxides and nickel oxides are more easily reduced than iron oxides, the timing of releasing oxygen is too early, and therefore, the effect of accelerating the degreasing is weak.

Next, experimental examples performed to determine the scope of the present invention and to confirm the effects of the present invention will be described.

[0042] Copper powder, Fe O powder as iron oxide powder, glass

twenty three

The powder and the organic vehicle were mixed and dispersed using a three-roll mill to obtain each of the conductive pastes of Samples 1-120.

[Table 1]

[0044] Note that, of Samples 1 to 20, Sample 1 and Sample 9, Sample 2 and Sample 10, Sample 3 and Sample 11, Sample 4 and Sample 12, Sample 5 and Sample 15, Sample 6 and Sample 18, and Sample Samples 7 and 19 have the same composition, but differ in the “baking peak temperature” described later.

[0045] In the column of "Fe O powder" in Table 1, the values shown in parentheses are the values of copper powder and Fe 2 O 3.

It shows the volume percentage of Fe 2 O 3 powder with respect to the total volume of 2 3 2 3 powder. In addition, Table 1

twenty three

The values in parentheses in the column of `` Powder '' are copper powder, Fe 2 O 3

Shows the volume percentage of glass powder with respect to the total volume of 23 powder and glass powder.

The glass powder has an average particle size of 2 μm and has a softening point of 530-560 ° C. A glass material made of zinc oxide-based glass was used. Further, as the organic vehicle, an organic vehicle obtained by dissolving an organic binder mainly composed of an acrylic resin in an organic solvent mainly composed of terbineol was used.

Next, a ceramic layer containing BaTiO as a main component and each having a thickness of 2 m was used.

Three

A multilayer body for a multilayer ceramic capacitor, on which an internal conductor film mainly composed of a capacitor was formed, was prepared. In order to obtain this laminate, a firing step at a temperature of 1200 to 1400 ° C. was performed in a reducing atmosphere.

[0048] Next, a conductive paste according to each of Samples 120 shown in Table 1 was applied to both ends of the laminate by dipping, and dried at a temperature of 150 ° C for 15 minutes. Baking in an N-O atmosphere with an oxygen concentration of lOOppm or less

twenty two

External electrodes were formed.

Here, as shown in the column of “baking peak temperature” in Table 2, the baking conditions of applying a maximum temperature of 820 ° C. for 10 minutes were applied to samples 18 and 18 and A baking condition of applying a maximum temperature of 880 ° C. for 10 minutes was applied.

Next, a nickel plating film was formed on the external electrodes by electroplating, and a tin plating film was further formed thereon to obtain a multilayer ceramic capacitor according to each sample.

Next, as shown in Table 2, regarding the multilayer ceramic capacitors according to the respective samples thus obtained, “reaction layer thickness”, “plating defect rate”, “denseness”, and “high temperature load” The test failure rate was evaluated.

[0052] The "thickness of the reaction layer" was determined by observing a cross section of the multilayer ceramic capacitor with a scanning electron microscope (SEM).

[0053] Regarding the "plating failure rate", the tin-coated film on the external electrode of the multilayer ceramic capacitor was peeled off, and the external electrode was observed with a stereoscopic microscope of 50 times. Those having exposed external electrodes containing copper as a main component were determined to be defective plating, and the incidence of such defective plating was determined.

Regarding “density”, the multilayer ceramic capacitor of each sample is impregnated with a fluorescent solution under vacuum, and then the tin plating film, nickel plating film and copper formed on the multilayer ceramic capacitor are mainly used. The external electrode as a component is electrolytically peeled off, and the fluorescent liquid that has reached the surface of the laminate is removed. It was evaluated by observation. When a fluorescent solution was observed, the density was poor and indicated by `` X '' in Table 2, and when no fluorescent solution was observed, the density was judged to be good and indicated by `` 2 '' in Table 2. Was.

[0055] The "high-temperature load test failure rate" was obtained in order to evaluate the reliability of the multilayer ceramic capacitor, and was obtained after applying a 9.5V DC voltage for 100 hours at a temperature of 105 ° C. When the insulation resistance of the multilayer ceramic capacitor was less than 10 ⁷ Ω, it was determined to be defective, and the occurrence rate of defective products among the 18 multilayer ceramic capacitors was calculated.

[Table 2]

[0057] In Tables 1 and 2, the samples numbered with * are out of the scope of the present invention.

First, as shown in Table 1, with respect to the glass powder content, in Samples 8 and 17, the glass powder contained 7.5% by volume of the conductive paste, ie, copper powder, Fe O As it contains more than 25% by volume, such as 30% by volume, based on the total volume of the powder and glass powder, a relatively large amount of glass components precipitate on the surface of the external electrode, as shown in Table 2. In addition, a high plating defect rate was shown.

[0059] On the other hand, in Sample 13, as shown in Table 1, 1.25% by volume based on the volume of the glass powder force conductive paste, that is, the total volume of copper powder, FeO powder, and glass powder.

twenty three

On the other hand, since it is less than 10% by volume, such as 5% by volume, the voids cannot be sufficiently filled by the glass component in the external electrode, and as shown in Table 2, the denseness is poor. The high temperature load test failure rate was high.

Next, regarding the content of the Fe 2 O 3 powder, as shown in Table 1, the sample 1

In 2 3 1 3 and 9 1 1 1, Fe O powder is not more than 0.4% by volume based on the volume of the conductive paste, that is, copper

twenty three

3% by volume, such as 2% by volume or less, based on the total volume of the powder and FeO powder

twenty three

Is full. Therefore, the effect of Fe O, which makes it easy to form a reaction layer, is hardly obtained.

twenty three

As shown in Table 2, only a thin reaction layer was formed, and excessive diffusion of copper in the conductive base into the internal conductor film could not be suppressed. Many cracks occurred, indicating a high failure rate in the high temperature load test.

[0061] In particular, referring to Table 2, when comparing Samples 13 and 9 with Samples 9-11, according to Sample 9-11 in which the baking peak temperature was increased to 880 ° C, the baking peak temperature was high. Although the compactness was improved compared with the samples 13 and 13 whose temperature was relatively low at 820 ° C, the failure rate of the high temperature load test was not so much improved.

[0062] On the other hand, as shown in Table 1, the content of FeO powder

By volume of the 2 3 2 3 end force conductive paste 10 volume ^_0/0, i.e., copper powder and Fe O

It contains more than 40% by volume, such as 50% by volume, based on the total volume of the 23 powder. As a result, as shown in Table 2, although the reaction layer was easily formed, the sintering of the external electrode was suppressed, and a high failure rate in the high-temperature load test, which was inferior in denseness, was exhibited.

[0063] On the other hand, as shown in Table 1, the content of Fe 2 O 3 powder was

2 3 2 3 3-40% by volume based on the total volume of powder, and the content of glass powder is 10-25% by volume based on the total volume of copper powder, FeO powder and glass powder. %

twenty three

Samples 4-1 7, 12, 14-1 16, 18 and 19 that meet the requirements and fall within the scope of the present invention And consider.

As shown in Table 2, among the samples within the scope of the present invention, samples 12, 14, 116, 18, and 19 to which a relatively high baking peak temperature of 880 ° C. was applied, As a result, a reaction layer having a sufficient thickness was formed, and good results were obtained even with respect to deviations in the plating failure rate, denseness, and high temperature load test failure rate.

On the other hand, as shown in Table 2, in Samples 4 to 7, the baking peak temperature was relatively low at 820 ° C., and therefore, particularly in Samples 5, 6, and 7, the denseness was poor and the high temperature load test failure was high. The rate was shown. By increasing the baking peak temperature to 880 ° C, as shown, while comparing these Samples 5, 6 and 7 with Samples 15, 18 and 19, which have the same composition as each other, , Compactness and high-temperature load test failure rate can both be improved.

As described above, by adding a predetermined amount of Fe 2 O powder to the conductive paste,

twenty three

It is possible to form an external electrode that is dense and gives good results in a high-temperature load test, while preventing the occurrence of poor defects.

[0067] This is because during the baking for forming the external electrode, FeO

twenty three

Titanium dissolved in the ceramic layer containing BaTiO as the main component

Three

This is because the dissolution and diffusion of the glass component in the external electrode improved the plating solution solubility of the glass component in the external electrode, and a reaction layer was formed at the interface between the ceramic layer and the external electrode. This is because the reaction layer prevented excessive diffusion of the external electrode component into the internal conductor film.

The reaction layer described above has acid resistance! This was confirmed by the fact that the reaction layer did not dissolve in the plating solution even when the cross section of the multilayer ceramic capacitor having the external electrodes formed was immersed in an acidic tin plating solution.

When the crystal structure of the reaction layer was analyzed by high-temperature XRD (X-ray diffraction), and the constituent elements were analyzed by SAM (scanning Auger electron microscope), the spinel containing nickel, zinc, titanium and iron It was confirmed that a crystalline phase having a structure was formed.

[0070] In the above experimental example, FeO powder was used as the iron oxide powder.

twenty three

The same effect can be obtained even when FeO powder is used.

3 4

In the above experimental example, the multilayer ceramic electronic component is a multilayer ceramic capacitor. Therefore, the case where the ceramic constituting the ceramic layer is composed mainly of BaTiO

Three

In addition to BaTiO-based ceramics, ceramics mainly composed of titanium-containing composite oxides

Three

The same effect can be obtained for all the multilayer ceramic electronic components having the lamic layer.

Claims

The scope of the claims

[1] A conductive paste used for forming external electrodes of a multilayer ceramic electronic component,

Contains copper powder, iron oxide powder, glass powder, and organic vehicle,

The iron oxide powder contains 3 to 40% by volume based on the total volume of the copper powder and the iron oxide powder,

Glass powder contains 10 to 25% by volume based on the total volume of copper powder, iron oxide powder and glass powder.

Conductive paste.

[2] A laminate comprising a plurality of laminated ceramic layers and an internal conductor film containing nickel as a main component and formed along an interface between the ceramic layers, and an electric current is applied to the internal conductor film. A multilayer ceramic electronic component comprising an external electrode mainly composed of copper, formed on an outer surface of the laminate so as to be electrically connected,

2. A multilayer ceramic electronic component, wherein the external electrode also has a sintered body obtained by sintering the conductive paste according to claim 1.

[3] Consisting of a plurality of stacked ceramic layers mainly composed of a composite oxide containing titanium and an internal conductor film mainly composed of nickel formed along the interface between the ceramic layers. And a multilayer ceramic electronic component comprising an external electrode containing copper as a main component and formed on an outer surface of the multilayer so as to be electrically connected to the internal conductor film. hand,

The external electrode includes, as a glass component, zinc borosilicate glass containing iron oxide and titanium oxide,

At the interface between the ceramic layer and the external electrode in contact with the ceramic layer, a reaction layer is formed by generating a crystal phase having a spinel structure containing nickel, zinc, titanium and iron.