JP4211783B2 - Conductive paste and multilayer ceramic electronic components - Google Patents

Description

  The present invention relates to a conductive paste and a multilayer ceramic electronic component, and in particular, a conductive paste suitably used for forming an external electrode of a multilayer ceramic electronic component, and an external electrode formed using the conductive paste. The present invention relates to a laminated ceramic electronic component.

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

  As shown in FIG. 1, a multilayer ceramic capacitor 1 includes a multilayer body 4 including a plurality of laminated ceramic layers 2 and a plurality of internal conductor films 3 formed along an interface between the ceramic layers 2. And 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, but is electrically connected to one external electrode 5. The internal conductor films 3 and the internal conductor films 3 electrically connected to the other external electrode 5 are alternately arranged in the stacking direction.

  On the external electrode 5, for example, a first plating film 6 made of nickel is formed for the purpose of improving solder wettability, heat resistance, etc., and a second plating film made of tin or solder is further formed thereon. 7 is formed.

  In such a multilayer ceramic capacitor 1, the external electrode 5 is usually 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 and baking it. Formed by.

  By the way, as a conductive component contained in the internal conductor film 3, a base metal, particularly nickel, has recently been increasingly used. Thus, when the internal conductor film 3 contains nickel as a main component, it is preferable to use copper powder as the conductive metal powder contained in the conductive paste used to form the external electrode 5 (for example, (See Patent Documents 1 and 2). This is because 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 when baking the conductive paste for forming 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.

  However, as described above, when the conductive paste for forming the external electrode 5 contains copper and the conductive paste for forming the internal conductor film 3 contains nickel, the external electrode 5 is formed. Therefore, when the conductive paste is baked, copper contained in the external electrode 5 may be excessively diffused into nickel contained in the internal conductor film 3.

  Such excessive diffusion of copper thickens the internal conductor film 3 and causes cracks in the laminate 4 due to the stress generated at that time. Cracks generated in the multilayer body 4 reduce the reliability of the multilayer ceramic capacitor 1.

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

  However, when the conductive paste is baked at a low temperature, the denseness of the external electrode 5 may not be sufficiently secured. Therefore, in the above-described plating process for forming the plating films 6 and 7, the plating solution passes through the open pores existing in the external electrode 5 or while dissolving the glass component contained in the external electrode 5. May deteriorate the electrical insulation of the ceramic layer 2.

In order to increase the denseness of the external electrode 5, it is sufficient to perform baking at a higher temperature. However, when baking is performed at such a high temperature, the copper internal conductor film 3 contained in the external electrode 5 as described above. In addition to causing problems due to excessive diffusion to the glass, the fluidity of the glass component contained in the external electrode 5 is increased, and this glass component is raised on the surface of the external electrode 5, so that the plating films 6 and 7 In the plating process for formation, defective plating may be caused.
JP 59-184511 A JP-A-11-97281

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

The present invention is first directed to a conductive paste used for forming an external electrode of a multilayer ceramic electronic component. The conductive paste according to the present invention contains copper powder, glass powder, and an organic vehicle, and is characterized by further containing Fe ₂ O ₃ powder in order to solve the technical problems described above. Then, _Fe 2 _{O 3} powder, based on the total volume of copper powder and Fe ₂ O ₃ powder contains 3 to 40 vol%, the glass powder, the total volume of copper powder, _Fe 2 _{O 3} powder and a glass powder In contrast, it is characterized by containing 10 to 25% by volume.

  The present invention also provides a laminate formed of a plurality of laminated ceramic layers and an inner conductor film mainly composed of nickel formed along an interface between the ceramic layers, and an electric current applied to the inner conductor film. In addition, the present invention is also directed to a multilayer ceramic electronic component including an external electrode mainly composed of copper, which is formed on the outer surface of the multilayer body so as to be connected electrically.

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

  The present invention also includes a plurality of laminated ceramic layers mainly composed of a composite oxide containing titanium, and an internal conductor film mainly composed of nickel formed along an interface between the ceramic layers. Also directed to a multilayer ceramic electronic component including an external electrode composed mainly of copper and formed on the outer surface of the multilayer body so as to be electrically connected to the internal conductor film. .

In the multilayer ceramic electronic component, according to the present invention, the external electrode is made of a sintered body obtained by sintering the conductive paste according to the present invention described above, and the glass component includes iron oxide and titanium oxide. A reaction layer that contains a spinel structure crystal phase containing nickel, zinc, titanium, and iron is formed at the interface between the ceramic layer and the external electrode in contact with it. It is characterized by having.

As described above, the conductive paste according to the present invention contains a predetermined amount of Fe ₂ O ₃ powder. The inclusion of Fe ₂ O ₃ brings the following effects when the conductive paste is used for forming the external electrodes of the multilayer ceramic electronic component.

First, Fe ₂ O ₃ contained in the conductive paste has an oxygen donating effect and is reduced during baking to release oxygen. This released oxygen promotes 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.

Further, during baking of the conductive paste, Fe ₂ O ₃ is dissolved in the glass component contained in the conductive paste, and thus the ceramic component provided in the laminate with the glass component in which Fe ₂ O ₃ is dissolved is configured. The ceramic which reacts reacts, and a reaction layer is formed at the interface between the ceramic layer and the external electrode in contact therewith.

  This reaction layer first prevents the components of the external electrode from excessively diffusing into the internal conductor film, and as a result, the copper contained in the external electrode is excessively diffused into, for example, nickel contained in the internal conductor film. As a result, the internal conductor film can be prevented from being thickened, and cracks can be hardly generated in the laminate.

In addition, the presence of the reaction layer effectively prevents the plating solution from entering the laminate. The above-described improvement in the density of the external electrode also contributes to the prevention of the penetration of the plating solution. Further, as described above, the dissolution resistance of the plating solution is improved by dissolving Fe ₂ O ₃ in the glass component in the conductive paste. The improvement of the plating solution solubility of the glass component also contributes to preventing the penetration of the plating solution.

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

FIG. 1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 as an example of a multilayer ceramic electronic component of interest to the present invention.
FIG. 2 is an enlarged sectional view schematically showing a portion A of the multilayer ceramic capacitor 1 shown in FIG. 1, and an external electrode 5 formed using the conductive paste according to the present invention. The reaction layer 8 formed at the interface with the ceramic layer 2 is illustrated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Ceramic layer 3 Internal conductor film 4 Laminated body 5 External electrode 6,7 Plating film 8 Reaction layer

  The conductive paste according to the present invention is used for forming an external electrode of a multilayer ceramic electronic component. Hereinafter, the 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. In addition, the description above is used for the description of the basic configuration of the multilayer ceramic capacitor 1.

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

The conductive paste contains Fe ₂ O ₃ powder in addition to copper powder, glass powder, and organic vehicle. Here, the copper powder is made of copper or a metal containing copper as a main component . Also, as the glass powder, for example it is preferably used consisting of borosilicate zinc glass.

The Fe ₂ O ₃ 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 Fe ₂ O ₃ powder. Furthermore, glass powder, copper powder, with respect to the total volume of _Fe 2 _{O 3} powder and glass powder, is adapted to contain 10-25 vol%.

  FIG. 2 is a cross-sectional view schematically showing an enlarged portion 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 reaction layer 8 is provided at the interface between the ceramic layer 2 provided in the laminate 4 and the external electrode 5 in contact with the ceramic layer 2. Is formed.

As the ceramic constituting the ceramic layer 2, for example, a ceramic whose main component is a composite oxide containing titanium such as BaTiO ₃ is used, and the internal conductor film 3 is mainly composed of nickel to form the external electrode 5. In the conductive paste used in the above, when the glass powder made of zinc borosilicate glass is used, the external electrode 5 is made of zinc borosilicate glass containing iron oxide and titanium oxide as glass components. In the reaction layer 8, it has been confirmed that a crystal phase having a spinel structure containing nickel, zinc, titanium, and iron is generated.

As described above, the content of Fe ₂ O ₃ powder in the conductive paste is limited to ₃ to 40% by volume with respect to the total volume of copper powder and Fe ₂ O ₃ powder for the following reason. .

That, _Fe in 2 _{O 3} content of the powder is less than 3 vol%, _Fe 2 _{O 3} powder the effect of inclusion of is not sufficiently exhibited. Therefore, the oxygen donating effect by Fe ₂ O ₃ is small, the degreasing of the conductive paste cannot be sufficiently promoted, and the denseness of the external electrode 5 cannot be sufficiently improved. In addition, a reaction layer due to a 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 3 contained in the external electrode 5. Excess diffusion into the inside cannot be suppressed, and cracks are likely to occur in the laminate 4.

On the other hand, when the content of the Fe ₂ O ₃ powder exceeds 40% by volume, the sintering of the copper powder in the conductive paste is suppressed, and the obtained external electrode 5 becomes in a porous state, resulting in a multilayer ceramic capacitor. The reliability of 1 is reduced.

In addition, 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 Fe ₂ O ₃ powder, and the glass powder. If it is less than%, the external electrode 5 cannot be sufficiently filled with the glass component in the external electrode 5, so that the external electrode 5 is in a porous state. This is because a relatively large amount of precipitates may cause plating defects.

In order to promote degreasing during baking of the conductive paste, it is conceivable to increase the oxygen concentration in the atmosphere during baking instead of the oxygen donating effect of the Fe ₂ O ₃ powder contained in the conductive paste. However, even if the oxygen concentration in the atmosphere is increased as described above, degreasing of the surface layer of the external electrode 5 may be promoted, but sufficient promotion of degreasing cannot be desired inside the external electrode 5.

Moreover, it can be considered that the glass component contained in the conductive paste contains Fe ₂ O ₃ instead of containing the Fe ₂ O ₃ powder in the conductive paste. However, Fe ₂ O ₃ in the glass component is less likely to be reduced in the baking process than Fe ₂ O ₃ contained as a powder in the conductive paste, and therefore the oxygen donating effect is low.

Further, instead of Fe ₂ O ₃ , it is conceivable to use an oxide (an oxide that is easily reduced) having a relatively high equilibrium oxygen partial pressure of a metal-oxide such as cobalt oxide or nickel oxide. Since cobalt and nickel oxide are more easily reduced than Fe ₂ O _3, the timing of releasing oxygen is too early, and therefore the effect of promoting degreasing is weak.

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

With volume percent as shown in Table 1, to obtain a copper powder, F e ₂ O ₃ powder, a glass powder and an organic vehicle were mixed and dispersed by a three-roll, a conductive paste according to each of the samples 1 to 20 It was.

  Among 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 7 and sample Each of Nos. 19 is the same in terms of composition, but has different “baking peak temperatures” described later.

The numerical values shown in parentheses in the column of “Fe ₂ O ₃ powder” in Table 1 indicate the volume% of the Fe ₂ O ₃ powder with respect to the total volume of the copper powder and the Fe ₂ O ₃ powder. The numerical values shown in parentheses in the column of “glass powder” in Table 1 indicate the volume percentage of the glass powder with respect to the total volume of the copper powder, the Fe ₂ O ₃ powder and the glass powder.

  Further, as the glass powder, one made of zinc borosilicate glass having an average particle diameter of 2 μm and a softening point of 530 to 560 ° C. was used. As the organic vehicle, an organic binder mainly composed of an acrylic resin was dissolved in an organic solvent mainly composed of terpineol.

Next, a multilayer body for a multilayer ceramic capacitor was prepared in which a ceramic layer mainly composed of BaTiO ₃ and a thickness of 2 μm and an internal conductor film composed mainly of nickel were formed. In order to obtain this laminated body, the baking process at the temperature of 1200-1400 degreeC was implemented in reducing environment.

Next, a conductive paste according to each of Samples 1 to 20 shown in Table 1 is applied to both ends of the laminate by immersion, and dried at a temperature of 150 ° C. for 15 minutes, and then an oxygen concentration of 100 ppm or less. Baking was performed in an N ₂ —O ₂ atmosphere to form an external electrode made of a sintered body of conductive paste.

  Here, as shown in the column of “baking peak temperature” in Table 2, the baking conditions for applying the maximum temperature of 820 ° C. for 10 minutes are applied to the samples 1 to 8, and the maximum temperature of 880 is applied to the samples 9 to 20. Baking conditions applying 10 ° C. for 10 minutes were applied.

  Next, a nickel plating film was formed on the external electrode 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, for the multilayer ceramic capacitors according to the respective samples thus obtained, “reaction layer thickness”, “plating failure rate”, “denseness”, and “high temperature load test failure rate” Was evaluated.

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

  Regarding the “plating failure rate”, with the tin plating film on the external electrode of the multilayer ceramic capacitor peeled off, the external electrode was observed with a stereo microscope at a magnification of 50 times, and the underlying copper of the nickel plating film was the main component. The case where the external electrode is exposed is determined as a defective plating product, and the occurrence rate of such defective plating products is obtained.

  For “denseness”, the multilayer ceramic capacitor of each sample is vacuum impregnated with a fluorescent solution, and then the tin plating film, nickel plating film, and external electrode mainly composed of copper formed on the multilayer ceramic capacitor are electrolyzed. Evaluation was made by observing the fluorescent solution that had peeled off and reached the surface of the laminate. When the fluorescent solution is recognized, the denseness is inferior and is indicated by “x” in Table 2. When the fluorescent solution is not recognized, the denseness is good and indicated by “◯” in Table 2. It was.

The “high temperature load test failure rate” is obtained in order to evaluate the reliability of the multilayer ceramic capacitor. The insulation of the multilayer ceramic capacitor after applying a 9.5 V DC voltage for 100 hours at a temperature of 105 ° C. A product having a resistance of less than 10 ⁷ Ω is determined as a defective product, and the occurrence rate of defective products in 18 multilayer ceramic capacitors is obtained.

  In Tables 1 and 2, the sample numbers marked with * are outside the scope of the present invention.

First, as shown in Table 1, regarding the content of the glass powder, in Samples 8 and 17, the glass powder was 7.5% by volume with respect to the volume of the conductive paste, that is, copper powder, Fe ₂ O _3. Since it contains more than 25% by volume, such as 30% by volume, with respect to the total volume of the powder and glass powder, a relatively large amount of glass component is deposited on the surface of the external electrode, as shown in Table 2. A high plating defect rate was exhibited.

On the other hand, in Sample 13, as shown in Table 1, the glass powder was 1.25% by volume with respect to the volume of the conductive paste, that is, the total volume of the copper powder, Fe ₂ O ₃ powder and glass powder. Therefore, the gap is not sufficiently filled with the glass component in the external electrode, such as 5% by volume, and as shown in Table 2, the denseness is inferior and the high temperature is high. The load test failure rate was shown.

Next, with respect to _Fe 2 _{O 3} powder content of, as shown in Table 1, in Sample 1-3 and 9 to 11, _Fe 2 _{O 3} powder, the volume of the conductive paste, 0.4 volume %, That is, less than 3% by volume, such as 2% by volume or less with respect to the total volume of the copper powder and the Fe ₂ O ₃ powder. Therefore, since the effect of Fe ₂ O ₃ that makes it easy to generate a reaction layer is hardly obtained or not obtained at all, only a thin reaction layer is formed as shown in Table 2, and the inside of the copper in the conductive paste Excessive diffusion into the conductor film could not be suppressed, and a large number of cracks occurred in the laminate, indicating a high high temperature load test failure rate.

  In particular, referring to Table 2, when comparing the samples 1 to 3 and the samples 9 to 11, according to the samples 9 to 11 in which the baking peak temperature was increased to 880 ° C., the baking peak temperature was 820 ° C. Compared to samples 1 to 3, which are relatively low, the density is improved, but the high-temperature load test failure rate cannot be improved so much.

On the other hand, with respect to _Fe 2 _{O 3} powder content of, as shown in Table 1, in Sample 20, _Fe 2 _{O 3} powder, the volume of the conductive paste, 10% by volume, i.e., copper powder and Fe ₂ the total volume of O ₃ powder, and so 50% by volume, containing more than 40 vol%. Therefore, as shown in Table 2, although the reaction layer was easily generated, sintering of the external electrode was suppressed, the denseness was poor, and a high high-temperature load test failure rate was exhibited.

For these, as shown in Table 1, _Fe 2 _{O 3} powder content is, the total volume of copper powder and _Fe 2 _{O 3} powder, 3 to 40 vol%, and a glass powder Samples 4 to 7, 12, and 14 in the scope of the present invention satisfying the condition that the content is 10 to 25% by volume with respect to the total volume of the copper powder, the Fe ₂ O ₃ powder, and the glass powder. Consider 16, 18, and 19.

  Among the above samples within the scope of the present invention, as shown in Table 2, samples 12, 14-16, 18 and 19 to which a relatively high baking peak temperature of 880 ° C. was applied, all have a sufficient thickness. The reaction layer was formed, and good results were shown for all of the defective plating rate, the denseness, and the high temperature load test defective rate.

  On the other hand, in Samples 4-7, as shown in Table 2, the baking peak temperature was relatively low at 820 ° C., so in Samples 5, 6 and 7 in particular, the denseness was inferior and showed a high high temperature load test failure rate . However, as can be seen by comparing these samples 5, 6 and 7 with samples 15, 18 and 19 having the same composition as these, if the baking peak temperature is increased to 880 ° C., the denseness and the high temperature load test are poor. Both rates can be improved.

As described above, by including a predetermined amount of Fe ₂ O ₃ powder in the conductive paste, an external electrode that is dense and brings good results in a high-temperature load test while preventing plating defects from occurring. Can be formed.

This is because, during baking for forming the external electrode, Fe ₂ O ₃ is dissolved in the glass component in the external electrode, and titanium contained in the ceramic layer mainly composed of BaTiO ₃ becomes the glass component in the external electrode. This is because dissolution and diffusion 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 excessive diffusion to the inner conductor film is prevented.

  In addition, the reaction layer mentioned above has acid resistance. This was confirmed from the fact that the reaction layer did not dissolve in the plating solution even when the cross section of the multilayer ceramic capacitor on which the external electrode was formed was immersed in an acidic tin plating solution.

  Further, 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 crystal phase of spinel structure containing nickel, zinc, titanium and iron It was confirmed that

In the above experimental example, the multilayer ceramic electronic component is a multilayer ceramic capacitor, and the ceramic constituting the ceramic layer is based on BaTiO ₃ as a main component. However, the ceramic component is not limited to the BaTiO ₃ system and contains titanium. The same effect can be obtained for all the multilayer ceramic electronic components in which the ceramic layer is composed of the ceramic mainly composed of the composite oxide.

Claims (3)

A conductive paste used for forming an external electrode of a multilayer ceramic electronic component,
Containing copper powder, Fe ₂ O ₃ powder, glass powder and organic vehicle,
Fe ₂ O ₃ powder, based on the total volume of copper powder and Fe ₂ O ₃ powder contains 3 to 40 vol%,
Glass powder, copper powder, with respect to the total volume of _Fe 2 _{O 3} powder and glass powder, containing 10 to 25 vol%,
Conductive paste. A laminated body composed of a plurality of laminated ceramic layers and an internal conductor film mainly composed of nickel formed along an interface between the ceramic layers, and electrically connected to the internal conductor film A multilayer ceramic electronic component comprising external electrodes mainly composed of copper, formed on the outer surface of the multilayer body as described above,
The said external electrode is a multilayer ceramic electronic component which consists of a sintered compact obtained by sintering the electrically conductive paste of Claim 1. A laminate comprising a plurality of laminated ceramic layers mainly composed of a composite oxide containing titanium, and an internal conductor film mainly composed of nickel formed along an interface between the ceramic layers. And a multilayer ceramic electronic component comprising external electrodes mainly composed of copper formed on the outer surface of the multilayer body so as to be electrically connected to the internal conductor film,
The external electrode is made of a sintered body obtained by sintering the conductive paste according to claim 1, and zinc borosilicate glass containing iron oxide and titanium oxide is used as a glass component. Including
At the interface between the ceramic layer and the external electrode in contact with the ceramic layer, a reaction layer is formed that generates a crystal phase having a spinel structure containing nickel, zinc, titanium, and iron.
Multilayer ceramic electronic components.

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