JP2002198253A - Ceramic electronic component and conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive paste which can prevent solder leakage and characteristic degradation due to temperature cycle test while preventing oxidization from reducing a capacity and while obtaining adhesion, in the case where the paste is used for a terminal electrode of a ceramic electronic component. SOLUTION: A laminated ceramic capacitor 10, in which a terminal electrode 4 is formed on an end face of a ceramic main body 1, comprises a base zinc layer 4a on an interface connected to the ceramic main body 1 of the terminal electrode 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic electronic component and a conductive metal paste for a terminal electrode thereof.

[0002]

2. Description of the Related Art In ceramic electronic components such as multilayer ceramic capacitors, conductive metal paste (hereinafter abbreviated as conductive paste) used for terminal electrodes is mainly made of copper or the like for cost reduction and higher frequency. It is used those with the component. This terminal electrode mixes a metal powder such as copper and a vehicle consisting of an organic binder and a solvent,
This is kneaded with a three-roll mill or the like to produce.
The baking of the terminal electrode is performed by baking in a reducing atmosphere in a range of 700 to 900 ° C.

However, according to the above-mentioned conductive paste, oxidation of copper during baking may result in insufficient connection with internal electrodes of electronic components or difficulty in solder mounting as terminal electrodes. .

Further, if no added glass frit, sintering among the metal powder in the internal terminal electrodes tends to become insufficient, to become a porous state, and the plating solution infiltration,
The connection with ceramic electronic components is affected by the intrusion of moisture from the outside, and the environment resistance is low.

Therefore, a conductive paste obtained by kneading a composite metal powder in which zinc is coated on the surface of a copper powder, a glass frit made of an inorganic compound, an organic binder and a solvent is disclosed in Japanese Patent Publication No. Hei 6-90882. It has been disclosed.

According to the same report, a metal powder composed of a glass frit, a copper core portion and a zinc coat portion is easily fixed by sintering. This copper core has a diameter of 0.5-1 μm.
Copper powder of about m, 0.1 to 0.2 in the copper core portion surface
A zinc coating is applied to about μm.

[0007] That is, by using zinc coated on the surface of copper powder as the metal powder for the conductive paste, the metal powder is easily sintered, and the zinc on the surface of copper powder diffuses into copper. It is possible to produce a sintered body with a high density by forming an alloy, and to prevent the surface of the copper terminal electrode from being oxidized.

Further, by adding a glass frit, the bonding strength between the terminal electrode and the ceramic body can be increased.

[0009]

However, the above-mentioned conductive paste has a drawback in that when the ceramic electronic component is mounted by soldering, poor solder wetting due to floating of the surface of the glass frit component occurs.

Conversely, the glass frit component melts and diffuses into the porcelain of the electronic component and becomes a starting point for cracks. Therefore, during a temperature cycle test, cracks occur at the interface between the terminal electrode and the porcelain, resulting in deterioration of characteristics. What happened.

The present invention has been devised in view of the above problems, and has as its object to prevent a decrease in capacity due to oxidation when used as a terminal electrode of a ceramic electronic component and to secure a fixing force. Another object of the present invention is to provide a conductive paste capable of preventing poor solder wetting and characteristic deterioration due to a temperature cycle test.

[0012]

A ceramic electronic component according to the present invention is a ceramic electronic component having a terminal electrode formed on an end face of a ceramic body, wherein the terminal electrode contains zinc as a main component at an interface bonded to the ceramic body. The present invention provides a ceramic electronic component having a layer having the following characteristics.

Further, the present invention provides a conductive paste obtained by kneading a metal powder obtained by coating a surface of a copper powder having a diameter of 1.5 to 3 μm with zinc with an organic binder and a solvent.

[0014]

Next, the present invention will be described with reference to the drawings. A description will be given of a multilayer ceramic capacitor as an example of the ceramic electronic component.

FIG. 1 is a longitudinal sectional view showing a state where a conductive paste constituting an external terminal electrode of the present invention is applied to the surface of a ceramic body and dried. FIG. 2 is a longitudinal sectional view showing a state where the conductive paste of FIG. 1 is sintered. Figure 3 is a longitudinal sectional view of the ceramic electronic component of the present invention.

[0016] In Figure, the laminated ceramic capacitor 10, 1 ceramic body, 2 is Ni internal electrode, 3 is the external terminal electrodes mainly composed of copper and zinc, 4 in the underlying layer, the underlying zinc layer 4a, It comprises an alloy layer 4b and a surface zinc layer 4c. Reference numeral 5 denotes an Ni-plated intermediate layer, reference numeral 6 denotes a Sn-plated surface layer, and the terminal electrodes are composed of an underlayer 4, an intermediate layer 5, and a surface layer 6.

Here, an underlying zinc layer 4a having a thickness of 0.01 to 1 μm is formed at an interface of the underlying layer 4 connected to the ceramic body 1. Further, the proportion of copper and zinc in the cross-sectional area of the underlayer 4 is 95% or more.

The conductive paste which is the material of the external terminal electrodes 3 includes a composite metal powder in which the surface of a copper core 3a is coated with a zinc coating 3b, and an organic binder resin in which an organic binder resin is dispersed in an organic solvent. A mixture with a vehicle is used.

Here, examples of the organic binder include acrylic resin, phenol resin, alkyd resin, rosin ester, ethyl cellulose, methyl cellulose, ethyl hydrocellulose, PVA (polyvinyl alcohol), polyvinyl butyrate and epoxy resin. Also,
Examples of the organic solvent include α-terpineol, BCA (butyl carbitol acetate), benzyl alcohol, and paraffin.

Among them, the use of ethyl cellulose as the organic binder resin is preferable in that it is completely dissolved in a petroleum ether solvent which does not dissolve in the resin because the binder resin of the ceramic green sheet is usually acrylic. Use of a petroleum ether-based solvent as the organic solvent is preferred in that ethyl cellulose having a high binding ability as a chain molecule can be sufficiently dissolved.

As described above, the conductive paste of the present invention uses a composite metal powder in which the surface of a copper core 3a having a diameter in the range of 1.5 to 3 μm is coated with a zinc coating 3b as a metal powder. If the diameter of the copper core portion 3a is less than 1.5 μm, internal stress is likely to be generated in the base layer 4 because the grain growth of the alloy layer 4b is too large, and the adhesion strength with the ceramic body 1 is reduced. On the other hand, when the diameter of the copper core portion 3a is larger than 3 μm, the film density is reduced and the underlayer 4 becomes porous, which may cause deterioration of characteristics in a wet and medium load test. It is.

The thickness of the zinc coating 3b is 0.1
It is desirably in the range of 0.3 μm. That is,
If the thickness is less than 0.1 μm, the amount of zinc at the interface with the ceramic main body 1 will be insufficient, and will be insufficient to cause the chemical bonding. On the other hand, if it is larger than 0.3 μm, the zinc coating 3b becomes a large wall with respect to the copper core, and the electric resistance of the electrode itself increases, which is not desirable.

The ceramic body 1 has a dielectric ceramic layer made of a dielectric material such as barium titanate and at least one or an alloy of at least one of nickel, copper, iron, cobalt, chromium and silver. The internal electrodes 2 having a rectangular planar shape are arranged so as to face each other.

According to the ceramic electronic component of the present invention, the glass frit conventionally added for improving the bonding between the ceramic body 1 and the underlayer 4 is not added. An underlayer 4 mainly composed of copper and zinc is formed on an end face of the ceramic body 1, and a thickness of 0.01 to 1 μm is formed on an interface of the underlayer 4 connected to the ceramic body 1.
This is because the underlying zinc layer 4a of m is formed.

That is, when the base layer 4 is baked, zinc moves to the interface between the ceramic main body 1 and the external terminal electrode 3 and oxidizes zinc. It is considered that a chemical bond is generated between the ceramic layers and the base layer 4 and the ceramic main body 1 are brought into close contact with each other without the glass frit interposed therebetween.
Therefore, since the base zinc layer 4a is formed, the bondability between the ceramic body 1 and the base layer 4 is sufficiently obtained, and the bondability between the ceramic body 1 and the base layer 4 is sufficiently obtained.

Further, since there is no need to add a glass frit which has been conventionally added, and plating defects due to surface floating of the glass frit component, diffused into the ceramic body 1 a glass frit component is melted, the starting point of cracks By doing so, it is possible to prevent the occurrence of cracks at the interface between the underlayer 4 and the ceramic body 1 during the temperature cycle test, thereby preventing the characteristics from deteriorating.

Here, the thickness of the underlying zinc layer 4a is 0.01
If it is less than μm, the bonding property between the ceramic main body 1 and the base layer 4 is insufficient, while if it exceeds 1 μm, the resistance of the terminal electrode itself is undesirably increased.

Further, in the ceramic electronic component of the present invention, since the glass frit is not added, the ratio of copper and zinc in the underlayer 4 can be 95% or more, and the conductor resistance as the external terminal electrode 3 is reduced. It becomes a ceramic electronic component suitable for a high frequency circuit.

Examples of the production method of the multilayer ceramic capacitor 10, the internal electrode 2 is formed, as shown in FIG. 1, when the conductive paste of the present invention is dried with the coating to the ceramic body 1, a copper core portion 3a in the ceramic body 1 And zinc coating part 3
The state is such that the metal powder of b is attached.

Next, when the conductive paste in the state shown in FIG. 1 is sintered at 700 ° C. to 900 ° C., the zinc coated portion 3b
Melts at the sintering temperature, moves to the interface between the underlayer 4 and the ceramic body 1 and the surface of the underlayer 4 as shown in FIG. 2, and is deposited so as to cover the alloy layer. The underlying zinc layer 4 a, which is a layer having a high thickness, is formed, and a surface zinc layer 4 c is formed on the surface of the underlying layer 4. In addition, an alloy layer 4b in which the surface of the copper particles is alloyed into brass is formed between the base zinc layer 4a and the surface zinc layer 4c. Then, a dense sintered body can be obtained.

The underlayer 4 is connected to each of the internal electrodes 2 extending to both ends of the ceramic body 1. Next, in order to obtain solder heat resistance on the surface of the underlayer 4,
The multilayer ceramic capacitor 10 of the present invention is manufactured by applying a 3 μm intermediate layer (Ni plating) 5 and further applying a surface layer (Sn plating) 6 having a thickness of 1 to 3 μm to obtain solder wettability on the surface. Is done.

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

The conductive paste of the present invention can be used not only for forming a ceramic capacitor but also for forming terminal electrodes of various electronic components such as a piezoelectric resonance component and a chip resistor.

[0034]

Hereinafter, examples of the present invention will be described together with comparative examples, and features thereof will be described in more detail.

First, a conductive paste is prepared. This is performed by blending a copper powder, a resin component, and a solvent and dispersing the mixture with a three-roll mill. Here, as the resin component, a cellulose resin is blended. As the solvent, benzyl alcohol and α-terpineol are used to prepare the conductive paste.
After applying the conductive paste to the ceramic body (see FIG. 1), the paste is dried at 170 ° C.
Then, the substrate is baked at a temperature of ° C. to form an underlayer 4 (see FIG. 2). In order to obtain solder heat resistance on the surface of the underlayer 4, a thickness of 1
An Ni plating 5 having a thickness of 1 to 3 μm is applied, and a Sn plating 6 having a thickness of 1 to 3 μm is applied on the surface to obtain solder wettability.
Thus, for example, a 2012 type multilayer ceramic capacitor 10 having a total length of 2 mm and a width of 1.2 mm is obtained (FIG. 3).
reference).

Sample No. 1 to 6 have a core of 1 to 4 μm
And the coating part was 0.2 μm zinc, and no glass frit was added.

Sample No. No. 7 did not form a coat portion and did not add glass frit.

Sample No. In No. 8, copper was 1 μm in the core and zinc was 0.2 μm in the coating, and 10 wt% of glass frit was added to the entire conductive paste.

With respect to the obtained sample, the presence or absence of cracks in the terminal electrode was confirmed.
A terminal electrode adhesion test, a flexural strength test, a solder wettability test, a wet load test, and a temperature cycle test were measured.

The presence or absence of cracks in the terminal electrode was determined by observing the end faces of 500 samples with a metallographic microscope and determining the rate at which cracks occurred.

The capacitance (Cap) is JIS C 64
Based on 29, using an impedance analyzer,
Measured under the conditions of 1 kHz, 1.0 Vrms, 1.0 μF
Those having the above conditions were regarded as good products, and those having less than 1.0 μF were regarded as defective products.

In the terminal electrode fixing force (shear strength) test, 22 samples were soldered to a glass epoxy substrate, and the ratio of the sample having a strength of less than 1 kg when a force was applied by a fixing pin was determined as a defective rate. .

The flexural strength test was performed according to JIS C 6429.
Based on the above, the sample is soldered on the glass epoxy board for the flexural strength test, the soldering surface of the sample is placed on the lower side, this board is placed on a support having a span of 90 mm, and a weight is applied to the upper face of the center of the span. The amount of flexure of the substrate when peeled from the substrate was measured, and those having a flexure amount of 1.5 mm or more were regarded as good products and those having a flexure amount of 2.0 mm or more were regarded as good non-defective products.

The solder wettability test was conducted after preheating 22 samples.
A non-defective product that is immersed in solder and has at least 95% of the surface area of the electrode part covered with new solder in the solder fillet appearance
Uncovered products were regarded as defective products, and the defective rate was determined.

In a wet load test, 100 samples were subjected to 65 ° C.
Under the conditions of 90 to 95% RH and DC 10 V, the insulation resistance of the sample taken out of the test tank was measured, and it was determined whether or not the resistance was low to determine whether the sample was defective.

The temperature cycle test was conducted according to JIS C510
Based on No. 2, 5 cycles of -55 to 125 ° C were performed,
55 ° C (30 minutes)-room temperature (10 minutes)-+ 125 ° C (30 minutes)
(Minutes) in order to leave it at the three stages of temperature, which constitutes one cycle. This operation is repeated for 5 cycles, and the capacitance, t
An δ, insulation resistance, and withstand voltage were checked for deterioration.

Table 1 shows the results. In Table 1, the sample No. Those marked with * are comparative examples.

[0048]

[Table 1]

As is clear from Table 1, a composite metal powder in which the surface of a copper powder having a diameter of 1.5 to 3 μm is coated with zinc was used as the metal powder, and no glass frit was added ( Sample Nos. 2 to 5), no cracks in terminal electrodes, capacitance of 100 nF, terminal electrode fixing force of 1 kg or more, flexural strength of 2.0 mm or more, poor solder wetting failure rate of 0%, wet NG load: 0%, temperature cycle NG is 0% defective-free multilayer ceramic capacitor comprising could be formed.

Here, such a good sample No. Two
For No. 5, the terminal electrode portion of the multilayer ceramic capacitor was polished, an SEM image was photographed, the thickness of the base zinc layer 4a was measured from the obtained SEM image, and the thickness was calculated by dividing by the magnification of the SEM image. As a result, the sample No. 2
It has been found that the thicknesses of the base zinc layers 4a to 5 are in the range of 0.01 to 1 μm.

On the other hand, when copper powder having a diameter of 1 μm was used (Sample No. 1), 20% of the terminal electrodes cracked during sintering.

When copper powder having a diameter of 4 μm was used (sample No. 6), 3/100 wet and medium loads NG occurred.

When zinc was not coated on the surface of the copper powder and no glass frit was added (sample N
o. In 7), the capacitance was 52 nF, the terminal electrode fixing force was 0.12 kg, the bending strength was 1.89 mm, and 25% of the temperature cycles NG occurred.

When the glass frit was added (Sample No. 8), the defective rate of solder wetting was 12%, and the temperature cycle NG was 45%. Sample No. When the terminal electrode portion of the multilayer ceramic capacitor of No. 1 was polished and an SEM image was observed, the thickness of the underlying zinc layer 4a was in the range of 0.01 to 1 μm, but was broken in some places. On the other hand, the sample No. In the case of No. 6, the thickness of the underlying zinc layer 4a was in the range of 0.01 to 1 [mu] m, but copper was detected in some places with the zinc coated. In addition, the sample No. In the case of No. 7, the underlying zinc layer 4a was not formed. In addition, the sample No. In the case of 8, the underlying zinc layer 4
a was not formed, copper was detected with zinc coated at the interface between the ceramic body and the underlayer, and glass frit was detected in some places.

[0055]

As described above, the ceramic electronic component of the present invention can prevent a decrease in capacity due to oxidation, can obtain desired values of fixing force and flexural strength, and can prevent characteristic deterioration due to a temperature cycle test. Can be prevented and even
Since it does not contain glass frit, plating defects due to floating glass and cracks on the ceramic electronic component surface layer can be prevented.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a state where a conductive paste of the present invention is applied to a surface of a ceramic body and dried.

FIG. 2 is a partial sectional view showing a state where the conductive paste of FIG. 2 is sintered.

FIG. 3 is a sectional view of the ceramic electronic component of the present invention.

[Explanation of symbols]

10 Ceramic electronic component (multilayer ceramic capacitor) 1 Ceramic body 2 Ni internal electrode 3a Copper core 3b Zinc coating 4 Base layer 4a Base zinc layer 4b ... alloy layer 4c ... surface zinc layer 5 ... intermediate layer (Ni plating) 6 ... surface layer (Sn plating)

Claims (2)

[Claims] 1. A ceramic electronic component in which a terminal electrode is formed on an end face of a ceramic body, wherein the terminal electrode has a layer containing zinc as a main component at an interface bonded to the ceramic body. parts. 2. A conductive paste obtained by kneading a metal powder obtained by coating a surface of a copper powder having a diameter of 1.5 to 3 μm with zinc with an organic binder and a solvent.