CN112786309A

CN112786309A - Paste for external electrode

Info

Publication number: CN112786309A
Application number: CN202011219717.7A
Authority: CN
Inventors: 塚本直德; 田中淳也; 西坂康弘
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2019-11-07
Filing date: 2020-11-04
Publication date: 2021-05-11
Anticipated expiration: 2040-11-04
Also published as: JP2021077750A; KR102366442B1; JP7192743B2; KR20210055596A; CN112786309B

Abstract

Provided is a paste for external electrodes, which can be prevented from having a shape in which the central portion swells when applied, compared with the end portions. The external electrode paste includes: a resin comprising at least a part of copolymerized ethyl cellulose-based resin and acrylic resin; a Cu filler; and a solvent, wherein an interfacial tension generated between the resin and the solvent is 15mN/m or more.

Description

Paste for external electrode

Technical Field

The present invention relates to an external electrode paste used for forming external electrodes of electronic components.

Background

Conventionally, a method of forming external electrodes of an electronic component such as a multilayer ceramic capacitor using an external electrode paste has been known. Such external electrode paste generally contains a resin as a binder, a metal filler and a solvent.

Patent document 1 describes a binder composition containing ethyl cellulose (Ethylcellulose) and an acrylic polymer, and describes that such a binder composition is used for producing a laminated ceramic capacitor or the like. The adhesive composition is a composition in which ethyl cellulose and an acrylic polymer are simply mixed.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-71986

When a conventional paste for external electrodes, such as the paste for external electrodes containing the binder composition described in patent document 1, is applied to a ceramic body, the central portion expands from the end portions due to the influence of surface tension and the like. Therefore, the formed external electrode has a convex shape with a thick central portion and thin end portions, and thus, the electronic component is difficult to be miniaturized.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide an external electrode paste that can be prevented from having a shape in which the central portion swells when applied, compared to the end portions.

Means for solving the problems

The external electrode paste according to the present invention is characterized by comprising: a resin comprising at least a portion of a copolymerized ethyl cellulose (Ethocel) based resin and an acrylic resin; a Cu filler; and a solvent, wherein an interfacial tension generated between the resin and the solvent is 15mN/m or more.

Effects of the invention

According to the paste for external electrodes of the present invention, the paste can be prevented from being expanded in the central portion as compared with the end portions when applied. Therefore, the electronic component manufactured using the external electrode paste of the present invention can be miniaturized.

Drawings

Fig. 1 is a view schematically showing the structure of a resin containing at least a partially copolymerized ethylcellulose-based resin and acrylic resin.

Fig. 2 is a graph showing a relationship between the weight% of an ethyl cellulose resin in a resin and an interfacial tension generated between the resin and a solvent.

Fig. 3 is a diagram for explaining a process of applying an external electrode paste to a ceramic body, in which fig. 3 (a) shows a state in which the ceramic body is immersed in the external electrode paste, fig. 3 (b) shows a state in which the ceramic body is lifted up, fig. 3 (c) shows a state in which an outward flow of the external electrode paste from the center portion to the end portions is generated, and fig. 3 (d) shows a state in which the external electrode paste is dried.

Fig. 4 is a view showing the external shape and the cutting position of the ceramic body used for the flatness test of the external electrode paste.

Fig. 5 (a) is a view schematically showing a cross section of a laminated ceramic capacitor in which external electrodes are formed using the external electrode paste of the present invention, and fig. 5 (b) is a view schematically showing a cross section of a laminated ceramic capacitor in which external electrodes are formed using a conventional external electrode paste.

Description of the reference numerals

10: ethyl cellulose

11: vinyl radical

20: acrylic resin

31: paste for external electrode

31 a: paste for external electrode adhered to ceramic body

32: ceramic body

40: ceramic body

41: end face

42: internal electrode

50a, 50 b: multilayer ceramic capacitor

51a, 51 b: ceramic body

52a, 52 b: an external electrode.

Detailed Description

The following describes embodiments of the present invention, and specifically describes the features of the present invention.

An external electrode paste according to one embodiment includes: a resin comprising at least a part of copolymerized ethyl cellulose-based resin and acrylic resin; a Cu filler; and a solvent, wherein an interfacial tension generated between the resin and the solvent is 15mN/m or more.

The ethylcellulose-based resin is at least 1 kind of ethylcellulose, methylcellulose, hydroxypropyl cellulose, trityl cellulose, acetyl cellulose, carboxymethyl cellulose and nitrocellulose, for example.

The acrylic resin is at least 1 kind of the group consisting of isobutyl methacrylate, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, n-butyl methacrylate and 2-ethylhexyl methacrylate.

The Cu filler is a particle containing at least one of Cu and a Cu alloy.

Examples of the solvent include terpineol, dihydroterpineol, dihydroterpinyl acetate, propylene glycol phenyl ether, benzyl alcohol, and the like,

At least 1 of ester alcohol and butyl carbitol acetate. The solvent species can be analyzed by measuring the generated gas by gas chromatography mass spectrometry. The gas chromatography mass spectrometry can be performed using, for example, a mass spectrometer 7890A/5975C (500 ℃ C. heating) manufactured by Agilent Technology, Inc.

As described above, at least a part of the ethylcellulose-based resin and the acrylic resin is copolymerized. For example, the OH group of the ethylcellulose resin is replaced by a vinyl group, and the ethylcellulose resin and the acrylic resin are bonded through the replaced vinyl group.

Fig. 1 is a view schematically showing the structure of a resin containing at least a partially copolymerized ethylcellulose-based resin and acrylic resin. Fig. 1 shows a schematic diagram of a case where the ethylcellulose-based resin is ethylcellulose 10. As shown in fig. 1, a part of ethyl cellulose 10 and a part of acrylic resin 20 are copolymerized. As described above, the OH group of the ethylcellulose 10 may be replaced by the vinyl group 11, and the ethylcellulose 10 and the acrylic resin 20 may be bonded via the replaced vinyl group 11. Further, at least a part of the ethylcellulose 10 is hydrogen-bonded.

Fig. 2 is a graph showing a relationship between the weight% of an ethyl cellulose resin in a resin and an interfacial tension generated between the resin and a solvent. In the external electrode paste according to the present embodiment, the interfacial tension generated between the resin and the solvent is 15mN/m or more. Since the interfacial tension generated between the resin and the solvent is 15mN/m or more, the force due to the difference in interfacial tension due to the Coffee-Ring Effect (Coffee-Ring Effect) to the outward flow becomes larger, and therefore, the fluidity is improved as compared with the conventional paste for external electrodes, and the paste can be prevented from being in a shape in which the central portion swells as compared with the end portions when applied.

In addition, when the proportion of the ethyl cellulose resin in the resin is 20% by weight or more and 50% by weight or less, the interfacial tension generated between the resin and the solvent becomes 40mN/m or more and less than 56mN/m, and the expansion of the central portion from the end portions can be more effectively suppressed when the paste for external electrodes is applied. Therefore, the interfacial tension generated between the resin and the solvent is preferably 40mN/m or more and less than 56 mN/m.

In addition, when the external electrode is formed using the external electrode paste containing the Cu filler, it is necessary to perform firing by lowering the oxygen partial pressure in order to suppress the generation of the bubble defect and to suppress the oxidation of Cu. That is, a resin that decomposes even with a small amount of oxygen is preferably used as the binder, and a resin containing a large amount of an acrylic resin is preferably used as such a resin.

Here, the interfacial tension generated between the resin and the solvent can be determined by the following method. First, a resin contained in the paste for external electrodes is applied on a glass substrate and dried, thereby obtaining a resin film. Next, using a contact angle meter, contact angles of pure water, diiodomethane, ethylene glycol with respect to the resin film were measured, and the surface free energy of the resin was calculated from the measured values. For example, a fully automatic contact angle meter "DMo-701" available from Kyowa interface science corporation can be used as the contact angle meter.

Next, the contact angle of the solvent with respect to the resin film was measured. Finally, the calculated surface free energy of the resin and the measured contact angle of the solvent are substituted into Dupre (dupler) formula and Young-Dupre formula, thereby calculating the interfacial tension.

Here, when an external electrode paste that contains only an ethyl cellulose resin and an acrylic resin without copolymerization is used, the dried coating film becomes brittle. Therefore, the chip-type electronic component coated with the external electrode paste may be chipped or peeled off from the dried coating film in the conveying step. This is considered to be caused by the following reason.

The dry coating film obtained by applying the paste for external electrodes, which contains a resin obtained by copolymerizing at least a part of an ethyl cellulose resin and an acrylic resin, has flexibility derived from the acrylic resin and rigidity derived from the ethyl cellulose resin, and has sufficient strength as the dry coating film.

On the other hand, in the external electrode paste containing an unpolymerized ethyl cellulose resin and an acrylic resin, in the kneading step with the Cu filler in the production process thereof, the phase separation of the acrylic resin and the ethyl cellulose resin is promoted, and therefore the glass powder segregates in the external electrode paste. It is considered that if an external force is applied to the dried coating film obtained by applying the paste for external electrodes, cracks easily develop from a brittle portion such as an interface between the glass segregated portion and Cu, which causes chipping and peeling. The chip electronic component can be detected by observing the appearance thereof with an optical microscope.

Fig. 3 is a diagram for explaining a step of applying the external-electrode paste 31 to the ceramic body 32 in the present embodiment.

First, the region of the ceramic body 32 where the external electrodes are to be formed is immersed in the external electrode paste 31 (see fig. 3 a), and then lifted (see fig. 3 b). The regions where the external electrodes are formed are, for example, both end surfaces of the ceramic body 32. Here, the paste for external electrodes adhering to the ceramic body 32 will be described with reference to 31 a. When the ceramic body 32 is pulled up, a Marangoni (Marangoni) convection occurs due to a temperature difference between the central portion and the end portion of the external-electrode paste 31a adhering to the ceramic body 32 and a concentration difference of the solute, as indicated by an arrow in fig. 3 (b). The solute is a Cu filler and a resin contained in the external electrode paste.

Since the amount of paste for external electrodes applied is smaller at the end portions than at the central portion, the drying of the end portions is more likely to progress. Therefore, the ratio of the resin in the paste for external electrodes is greater at the end portions than at the central portion, and becomes unstable in energy, and an outward flow of the paste for external electrodes from the central portion to the end portions occurs (see fig. 3 (c)). The outward flow is generated during a period in which the resin concentration at the end portion is higher than that at the central portion. Further, it is considered that if the drying progresses, the interface between the solute and the solvent increases, and the larger the interfacial tension at this time, the more unstable the energy becomes, and the outward flow becomes stronger.

Here, since the ethylcellulose-based resin has rigidity and high heat storage property, it plays a role of suppressing solidification of the paste for the external electrode during flowing and promoting outward flow in the drying step. Since a strong outward flow is generated, the paste for the external electrode flows from the central portion to the end portions, and thus the paste for the external electrode can be prevented from being in a shape that expands outward at the central portion (see fig. 3 (d)).

That is, in the paste for external electrodes according to the present embodiment, since the force of the outward flow becomes larger by setting the interfacial tension generated between the resin and the solvent to 15mN/m or more, the fluidity is improved as compared with the conventional paste for external electrodes, and the paste can be prevented from being in a shape in which the central portion swells as compared with the end portions. Therefore, the electronic component manufactured using the paste for external electrodes in the present embodiment can be downsized.

Fig. 5 (a) is a schematic cross-sectional view of a multilayer ceramic capacitor 50a in which external electrodes 52a are formed on a ceramic body 51a using the external-electrode paste according to the present embodiment. Fig. 5 (b) is a schematic cross-sectional view of a multilayer ceramic capacitor 50b in which external electrodes 52b are formed on a ceramic green body 51b using a conventional external electrode paste.

As shown in fig. 5 (b), the external electrode 52b formed using the conventional external electrode paste has a convex shape with a thick central portion and thin end portions. In contrast, the external electrode 52a formed using the external-electrode paste of the present embodiment has a flat shape, and can be prevented from having a convex shape as described above. Therefore, the multilayer ceramic capacitor in which the external electrodes are formed using the external electrode paste of the present embodiment can be downsized. In addition, when compared with the same size, the external electrode can be made thinner and the internal element can be made larger, so that the capacitance can be increased.

The method of applying the paste for an external electrode in the present embodiment to the ceramic body is not limited to the above-described impregnation with the paste for an external electrode.

Table 1 shows the results of examining the flatness of the external electrode paste when the average particle diameter D50 of the Cu filler contained in the external electrode paste and the ratio of nonvolatile components other than the solvent contained in the external electrode paste in the present embodiment were changed.

[ TABLE 1 ]

The average particle diameter D50 of the Cu filler contained in the external electrode paste was changed within a range of 0.3 to 8.0 μm. The average particle diameter D50 of the glass contained in the external electrode paste was 1.0. mu.m. The proportion of nonvolatile components other than the solvent contained in the paste for external electrodes is changed within a range of 5 vol% to 40 vol%. The external electrode paste had a PVC (Pigment Volume Concentration) of 56%. The ratio of the ethyl cellulose resin to the acrylic resin contained in the external electrode paste was set to 5: 5 by weight.

The flatness of the external electrode paste was examined by the following method. First, as shown in fig. 4, a ceramic body 40 having a dimension in the longitudinal direction L of 1.0mm, a dimension in the width direction W of 0.5mm, and a dimension in the thickness direction T of 0.5mm was prepared. The ceramic body 40 is a ceramic body constituting a laminated ceramic capacitor after the external electrodes are formed, and is a ceramic body obtained by firing a laminated body in which a plurality of ceramic green sheets coated with the internal electrode paste are laminated. The internal electrodes 42 are exposed at the end face 41 of the ceramic body 40 and the end face opposite to the end face 41 in the longitudinal direction L.

The end face 41 of the prepared ceramic body 40 is immersed in the paste for external electrodes, and then the applied paste for external electrodes is dried. Then, differences in the film thickness of the external electrode paste when the ceramic body 40 was cut along the cutting lines A-A and B-B shown in FIG. 4 were examined. More specifically, the difference between the film thickness of the thickest part of the film thickness of the external electrode paste at the position where the ceramic body 40 is cut along the a-a cutting line and the film thickness of the thinnest part of the film thickness of the external electrode paste at the position where the ceramic body 40 is cut along the B-B cutting line was examined. The film thickness of the thickest portion of the film thicknesses of the external electrode pastes cut along the a-a cutting line is the film thickness at the center portion in the thickness direction T. The thickness of the thinnest portion of the external electrode paste at the position cut along the B-B cutting line is the thickness at the end in the thickness direction T.

Here, the a-a cutting line is a cutting line when cutting along a plane defined by the longitudinal direction L and the thickness direction T at the center of the ceramic body 40 in the width direction W. The B-B cut line is a line parallel to the a-a cut line, and is a cut line at the position of the end of the internal electrode 42 in the width direction W of the ceramic body 40. The position of the B-B cutting line is, for example, 30 μm inward from the end in the width direction of the ceramic body 40 in the width direction W.

Here, when the film thickness of the thinnest portion of the film thickness of the external electrode paste at the position cut along the B-B cutting line is 0.5 μm or more, the difference between the film thicknesses is 16 μm or less, and there is no region where the external electrode paste is not applied to the end face of the ceramic body 40, it is determined as a good product (o), and the other portions are determined as a defective product (x).

As shown in table 1, when the nonvolatile content of the external electrode paste excluding the solvent was 15 vol% or more and 32 vol% or less, a desired good product coated with the external electrode paste was obtained regardless of the average particle diameter D50 of the Cu filler. Therefore, the proportion of nonvolatile components other than the solvent contained in the paste for external electrodes is preferably 15 vol% or more and 32 vol% or less. The average particle diameter D50 of the Cu filler is preferably in the range shown in table 1, that is, 0.3 μm or more and 8.0 μm or less.

As shown in table 1, when the nonvolatile content of the external electrode paste excluding the solvent is 10 vol%, the average particle diameter D50 of the Cu filler is preferably 0.3 μm or more and 2.0 μm or less. When the nonvolatile content of the external electrode paste excluding the solvent is 35 vol%, the average particle diameter D50 of the Cu filler is preferably 5.0 μm or more and 8.0 μm or less.

Here, in order to prevent oxidation, improve dispersibility, and the like, it is preferable that C is polymerized on the surface of the Cu filler. Table 2 shows the results of C polymerization on the surface of the Cu filler in the external electrode paste according to the present embodiment, and the results of examining the flatness of the external electrode paste when the amount of C polymerized was changed.

[ TABLE 2 ]

The average particle diameter D50 of the Cu filler is 0.05 to 1.0 [ mu ] m, and the amount of C polymerized on the surface of the Cu filler is changed within the range of 0.03 to 1.33 wt%. The average particle diameter D50 of the glass contained in the external electrode paste was 0.5. mu.m. The external electrode paste contained 20 vol% of nonvolatile components other than the solvent and 80 vol% of the solvent. The ratio of the ethyl cellulose resin to the acrylic resin contained in the external electrode paste was set to 5: 5 by weight.

The flatness of the external electrode paste was examined by the method described with reference to fig. 4. Here, the above-described difference in film thickness, i.e., the difference in film thickness of the external electrode paste when the ceramic body 40 is cut along each of the a-a cut line and the B-B cut line, is 16 μm or less, and is determined as a good product (o), and the case of 14 μm or less is determined as a good product (x).

As shown in table 2, the flatness of the paste for external electrodes was ensured as long as the amount of C polymerized on the surface of the Cu filler was in the range of at least 0.03 wt% to 1.33 wt%. Therefore, the amount of C polymerized on the surface of the Cu filler is preferably 0.03 wt% or more and 1.33 wt% or less. In addition, when the amount of C polymerized on the surface of the Cu filler is 0.11 wt% or more and 0.98 wt% or less, the flatness of the paste for external electrodes is further improved. Therefore, the amount of C polymerized on the surface of the Cu filler is more preferably 0.11 wt% or more and 0.98 wt% or less.

The present invention is not limited to the above-described embodiments, and various applications and modifications can be made within the scope of the present invention.

Claims

1. An external electrode paste, comprising:

a resin comprising at least a part of copolymerized ethyl cellulose-based resin and acrylic resin;

a Cu filler; and

a solvent, a water-soluble organic solvent,

an interfacial tension generated between the resin and the solvent is 15mN/m or more.

2. The paste for external electrodes according to claim 1,

an interfacial tension generated between the resin and the solvent is 40mN/m or more and less than 56 mN/m.

3. The paste for external electrodes according to claim 1 or 2,

c is polymerized on the surface of the Cu filler,

the amount of C polymerized on the surface of the Cu filler is 0.11 to 0.98 wt%.

4. The paste for external electrodes according to any one of claims 1 to 3,

the Cu filler is particles containing at least one of Cu and a Cu alloy, and has an average particle diameter D50 of 8 [ mu ] m or less.

5. The paste for external electrodes according to any one of claims 1 to 4,

the proportion of nonvolatile components other than the solvent contained in the paste for external electrodes is 15 vol% or more and 32 vol% or less.

6. The paste for external electrodes according to any one of claims 1 to 5,

the solvent comprises terpineol, dihydroterpineol, dihydroterpinyl acetate, propylene glycol phenyl ether, benzyl alcohol,

At least 1 of ester alcohol and butyl carbitol acetate.