JP7192743B2 - External electrode paste - Google Patents

Description

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

Conventionally, a method of forming external electrodes of an electronic component such as a multilayer ceramic capacitor using an external electrode paste is 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 and an acrylic polymer, and describes the use of such a binder composition for manufacturing laminated ceramic capacitors and the like. This binder composition is simply a mixture of ethyl cellulose and an acrylic polymer.

JP 2013-71986 A

When a conventional external electrode paste, such as the external electrode paste containing the binder composition described in Patent Document 1, is applied to a ceramic body, the central portion expands compared to the end portions due to the effects of surface tension and the like. . Therefore, the formed external electrode has a convex shape with a thick central portion and thin end portions, which makes it difficult to miniaturize the electronic component.

An object of the present invention is to solve the above problems, and to provide an external electrode paste capable of suppressing a shape in which the central portion swells more than the end portions when coated. .

The external electrode paste of the present invention is an external electrode paste used for forming external electrodes of multilayer ceramic electronic components,
a resin containing an ethyl cellulose -based resin and an acrylic resin, at least a part of which is copolymerized;
Cu filler;
a solvent;
glass powder and
including
The interfacial tension generated between the resin and the solvent is 15 mN/m or more ,
A ratio of non-volatile components other than the solvent contained in the external electrode paste is 15 vol % or more and 32 vol % or less .

According to the external electrode paste of the present invention, when applied, it is possible to prevent the central portion from expanding more than the end portions. Therefore, it is possible to reduce the size of electronic components manufactured using the external electrode paste of the present invention.

FIG. 2 is a diagram schematically showing the structure of a resin containing an ethyl cellulose -based resin and an acrylic resin, at least a part of which is copolymerized. FIG. 4 is a diagram showing the relationship between the weight percent of ethyl cellulose resin in the resin and the interfacial tension generated between the resin and the solvent. FIG. 4 is a drawing for explaining the process of applying the external electrode paste to the ceramic body, (a) showing a state in which the ceramic body is immersed in the external electrode paste, and (b) showing the ceramic body. (c) shows an outward flow in which the external electrode paste flows from the center to the end, and (d) shows a dried state of the external electrode paste. FIG. 4 is a diagram showing the external shape and cutting position of a ceramic body used when examining the flatness of the external electrode paste. (a) is a diagram schematically showing a cross section of a multilayer ceramic capacitor in which external electrodes are formed using the paste for external electrodes of the present invention, and (b) is a diagram showing external electrodes formed using a conventional paste for external electrodes. 1 is a diagram schematically showing a cross section of a laminated ceramic capacitor in which .

Embodiments of the present invention will be shown below to specifically describe features of the present invention.

The external electrode paste in one embodiment is an external electrode paste used for forming external electrodes of a multilayer ceramic electronic component, and is at least partially copolymerized with an ethyl cellulose resin and an acrylic resin. , a Cu filler, a solvent, and glass powder, the interfacial tension generated between the resin and the solvent is 15 mN/m or more, and the non-volatile components other than the solvent contained in the external electrode paste The ratio is 15 vol % or more and 32 vol % or less .

Ethyl cellulose -based resin is, for example, at least one of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, trityl cellulose, acetyl cellulose, carboxymethyl cellulose, and nitro cellulose.

The acrylic resin is, for example, at least one of isobutyl methacrylate, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, n-butyl methacrylate, and 2-ethylhexyl methacrylate.

Cu fillers are particles made of at least one of Cu and Cu alloys.

Solvents include, for example, at least one of terpineol, dihydroterpineol, dihydroterpinyl acetate, propylene glycol phenyl ether, benzyl alcohol, texanol, and butyl carbitol acetate. Solvent species can be analyzed by measuring the evolved gas by gas chromatography-mass spectrometry. Gas chromatography-mass spectrometry can be performed, for example, using a mass spectrometer 7890A/5975C (heated at 500° C.) manufactured by Agilent Technologies.

As described above, the ethyl cellulose resin and the acrylic resin are at least partially copolymerized. As an example, the OH group of the ethyl cellulose resin is substituted with a vinyl group, and the ethyl cellulose resin and the acrylic resin are bonded via the substituted vinyl group.

FIG. 1 is a diagram schematically showing the structure of a resin containing an ethyl cellulose resin and an acrylic resin, at least a part of which is copolymerized. FIG. 1 shows a schematic diagram when the ethyl cellulose resin is ethyl cellulose 10 . As shown in FIG. 1, part of the ethyl cellulose 10 and part of the acrylic resin 20 are copolymerized. As described above, the OH groups of the ethyl cellulose 10 may be substituted with the vinyl groups 11, and the ethyl cellulose 10 and the acrylic resin 20 may be bonded via the substituted vinyl groups 11. At least part of the ethyl cellulose 10 is hydrogen-bonded.

FIG. 2 is a diagram showing the relationship between the weight percent of ethyl cellulose resin in the resin and the interfacial tension generated between the resin and the solvent. The external electrode paste in this embodiment has an interfacial tension of 15 mN/m or more between the resin and the solvent. When the interfacial tension generated between the resin and the solvent is 15 mN/m or more, the force of the outward flow due to the interfacial tension difference generated by the coffee ring effect is increased, so compared to the conventional external electrode paste, Fluidity is improved, and when coated, it is possible to suppress a shape in which the central portion is swollen compared to the end portions.

Further, when the ratio of the ethyl cellulose resin in the resin was 20% by weight or more and 50% by weight, the interfacial tension generated between the resin and the solvent was 40 mN/m or more and less than 56 mN/m, and the external electrode paste was applied. In some cases, it is possible to more effectively suppress a shape in which the center portion swells more than the end portions. Therefore, the interfacial tension generated between the resin and the solvent is preferably 40 mN/m or more and less than 56 mN/m.

When the external electrodes are formed using an external electrode paste containing a Cu filler, in order to suppress the occurrence of blister defects and to suppress the oxidation of Cu, it is necessary to lower the partial pressure of oxygen during baking. There is That is, it is preferable to use a resin that decomposes even in a small amount of oxygen as the binder, and as such a resin, it is preferable to use a resin containing a large amount of acrylic resin.

Here, the interfacial tension generated between the resin and solvent can be obtained by the following method. First, a resin film is obtained by applying a resin contained in the external electrode paste onto a glass substrate and drying it. Subsequently, using a contact angle meter, the contact angles of pure water, diiodomethane, and ethylene glycol with respect to the resin film are measured, and the surface free energy of the resin is calculated from the measured values. As the contact angle meter, for example, a fully automatic contact angle meter "DMo-701" manufactured by Kyowa Interface Science Co., Ltd. can be used.

Subsequently, the contact angle of the solvent with respect to the resin film is measured. Finally, the interfacial tension is calculated by substituting the calculated surface free energy of the resin and the measured contact angle of the solvent into the Dupre's formula and the Young-Dupre's formula.

Here, when an external electrode paste that does not undergo copolymerization and simply contains an ethyl cellulose resin and an acrylic resin is used, the dry coating film becomes brittle. Therefore, chip-type electronic components coated with such an external electrode paste may suffer chipping or peeling of the dry coating film during the transportation process. This is considered to be due to the following reasons.

A dry coating film obtained by applying an external electrode paste containing a resin in which at least a portion of an ethylcellulose -based resin and an acrylic resin are copolymerized has the flexibility derived from the acrylic resin and the flexibility derived from the ethylcellulose -based resin. It has rigidity and sufficient strength as a dry coating film.

On the other hand, the external electrode paste containing an ethyl cellulose resin and an acrylic resin that are not copolymerized undergoes phase separation between the acrylic resin and the ethyl cellulose resin in the kneading step with the Cu filler in the manufacturing process. As a result, the glass powder segregates in the external electrode paste. When an external force is applied to the dry coating film obtained by applying this external electrode paste, cracks tend to develop from fragile portions such as the interface between the glass segregation portion and Cu, and this is thought to cause chipping and peeling. be done. Chipping or peeling of the external electrodes of the chip-type electronic component can be detected by observing the external appearance with an optical microscope.

FIG. 3 is a diagram for explaining the process of applying the external electrode paste 31 to the ceramic body 32 in this embodiment.

First, the regions of the ceramic body 32 where the external electrodes are to be formed are immersed in the external electrode paste 31 (see FIG. 3(a)) and then pulled out (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 external electrode paste adhered to the ceramic body 32 will be described as 31a. When the ceramic body 32 is pulled up, the external electrode paste 31a adhering to the ceramic body 32 changes in temperature and solute concentration between the central portion and the end portions as indicated by the arrows in FIG. 3(b). , Marangoni convection occurs. The solute is Cu filler and resin contained in the external electrode paste.

Since the coating amount of the external electrode paste is smaller in the end portion than in the center portion, the end portion is more likely to be dried. Therefore, the proportion of the resin in the external electrode paste is greater at the ends than at the center, and the energy becomes unstable. occurs (see FIG. 3(c)). This outward flow occurs while the resin concentration at the edges is higher than that at the center. As the drying progresses, the number of interfaces between the solute and the solvent increases, and the higher the interfacial tension at this time, the more unstable the energy becomes, and the stronger the outward flow becomes.

Here, since the ethyl cellulose resin has rigidity and high heat storage property, it suppresses hardening of the external electrode paste during the flow in the drying process, and plays a role of promoting the outward flow. The strong outward flow causes the external electrode paste to flow from the central portion to the end portions, so that it is possible to suppress the external electrode paste from swelling outward in the central portion (see FIG. 3). (d)).

That is, the external electrode paste of the present embodiment has an interfacial tension of 15 mN/m or more between the resin and the solvent, so that the force of the outward flow described above is increased. The fluidity is improved as compared with , and it is possible to suppress a shape in which the central portion is swollen compared to the end portions. Therefore, it is possible to miniaturize an electronic component manufactured using the external electrode paste of the present embodiment.

FIG. 5A 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 of the present embodiment. FIG. 5(b) is a diagram schematically showing a cross section of a laminated ceramic capacitor 50b in which external electrodes 52b are formed on a ceramic body 51b using a conventional external electrode paste.

As shown in FIG. 5B, the external electrode 52b formed using the conventional external electrode paste has a convex shape with a thick central portion and thin end portions. On the other hand, the external electrodes 52a formed using the external electrode paste in the present embodiment have a flat shape, and are 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 in this embodiment can be miniaturized. In addition, when compared with the same size, the external electrodes can be made thinner and the internal elements can be made larger, so that the capacity can be increased.

It should be noted that the method of applying the external electrode paste to the ceramic body in the present embodiment is not limited to the immersion in the external electrode paste described above.

Table 1 shows the values of the external electrode paste when the average particle size D50 of the Cu filler contained in the external electrode paste in the present embodiment and the ratio of non-volatile components other than the solvent contained in the external electrode paste are changed. The results of examining the flatness are shown.

The average particle diameter D50 of the Cu filler contained in the external electrode paste was changed within the range of 0.3 μm or more and 8.0 μm or less. The average particle size D50 of the glass contained in the external electrode paste is 1.0 μm. In addition, the ratio of the non-volatile components other than the solvent contained in the external electrode paste was changed within the range of 5 vol % or more and 40 vol % or less. PVC (Pigment Volume Concentration) of the external electrode paste is 56%. The weight ratio of the ethyl cellulose resin and the acrylic resin contained in the external electrode paste was 5:5.

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 length direction L of 1.0 mm, a dimension in the width direction W of 0.5 mm, and a dimension in the thickness direction T of 0.5 mm is prepared. This ceramic body 40 constitutes a laminated ceramic capacitor after the formation of the external electrodes, and is obtained by sintering a laminate obtained by laminating a plurality of ceramic green sheets coated with internal electrode paste. The internal electrodes 42 are exposed on the end surface 41 of the ceramic body 40 and the end surface located on the opposite side of the end surface 41 in the length direction L. As shown in FIG.

After the end face 41 of the prepared ceramic body 40 was immersed in the external electrode paste, the applied external electrode paste was dried. Then, the difference in film thickness of the external electrode paste was examined when the ceramic body 40 was cut along the AA and BB cutting lines shown in FIG. More specifically, the thickness of the thickest part of the thickness of the external electrode paste at the position where the ceramic body 40 is cut along the AA cutting line, and the thickness of the ceramic body 40 at the BB cut The difference between the film thickness of the thinnest portion of the film thickness of the external electrode paste at the position cut along the line was examined. Of the thicknesses of the external electrode paste cut along the AA cutting line, the thickness at the thickest portion is the thickness at the central portion in the thickness direction T. As shown in FIG. The thickness of the thinnest part of the thickness of the external electrode paste at the position cut along the BB cutting line is the thickness at the end in the thickness direction T. As shown in FIG.

Here, the AA cutting line is the cutting line along the plane defined by the length direction L and the thickness direction T at the center position of the width direction W of the ceramic body 40 . Further, the BB cutting line is a line parallel to the AA cutting line and is a cutting 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 BB cutting line is, for example, a position 30 μm inside in the width direction W from the end of the ceramic body 40 in the width direction.

Here, among the film thicknesses of the external electrode paste at the position cut along the BB cutting line, the film thickness of the thinnest portion is 0.5 μm or more, and the difference in film thickness is 16 μm or less. When there was no external electrode paste coated region on the end surface of the ceramic body 40, it was judged as a non-defective product (○), and other products were judged as a defective product (x).

As shown in Table 1, when the ratio of non-volatile components other than the solvent contained in the external electrode paste is 15 vol% or more and 32 vol% or less, the desired external electrode paste is obtained regardless of the average particle size D50 of the Cu filler. A good product coated with was obtained. Therefore, the ratio of the non-volatile components other than the solvent contained in the external electrode paste is preferably 15 vol % or more and 32 vol % or less. Also, the average particle size 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.

Further, as shown in Table 1, when the ratio of non-volatile components other than the solvent contained in the external electrode paste is 10 vol%, the average particle diameter D50 of the Cu filler is 0.3 μm or more and 2.0 μm or less. is preferred. Moreover, when the ratio of the non-volatile components other than the solvent contained in the external electrode paste 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, etc., it is preferable that C is polymerized on the surface of the Cu filler. Table 2 shows the results of examining the flatness of the external electrode paste according to the present embodiment when C is polymerized on the surface of the Cu filler and the amount of polymerized C is changed.

The average particle size D50 of the Cu filler is 0.05 μm or more and 1.0 μm or less, and the amount of C polymerized on the surface of the Cu filler is changed in the range of 0.03% by weight or more and 1.33% by weight or less. did. The average particle diameter D50 of the glass contained in the external electrode paste is 0.5 μm. The ratio of non-volatile components other than the solvent contained in the external electrode paste was 20 vol %, and the ratio of the solvent was 80 vol %. The weight ratio of the ethyl cellulose resin and the acrylic resin contained in the external electrode paste was 5:5.

The flatness of the external electrode paste was examined by the method described with reference to FIG. Here, the film thickness difference described above, that is, the difference in film thickness of the external electrode paste when the ceramic body 40 is cut along each of the AA cutting line and the BB cutting line is 16 μm or less. When the thickness was 14 μm or less, it was judged to be an excellent product (⊚).

As shown in Table 2, when the amount of C polymerized on the surface of the Cu filler is at least in the range of 0.03% by weight to 1.33% by weight, the flatness of the external electrode paste is ensured. be. Therefore, the amount of C polymerized on the surface of the Cu filler is preferably 0.03% by weight or more and 1.33% by weight or less. Further, when the amount of C polymerized on the surface of the Cu filler was 0.11% by weight or more and 0.98% by weight or less, the flatness of the external electrode paste was further improved. Therefore, the amount of C polymerized on the surface of the Cu filler is more preferably 0.11% by weight or more and 0.98% by weight or less.

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

10 Ethyl cellulose 11 Vinyl group 20 Acrylic resin 31 External electrode paste 31a External electrode paste adhered to ceramic element 32 Ceramic element 40 Ceramic element 41 End face 42 Internal electrodes 50a, 50b Multilayer ceramic capacitors 51a, 51b Ceramic element 52a, 52b external electrodes

Claims (4)

An external electrode paste used to form an external electrode of a multilayer ceramic electronic component,
a resin containing an ethyl cellulose -based resin and an acrylic resin, at least a part of which is copolymerized;
Cu filler;
a solvent;
glass powder and
including
The interfacial tension generated between the resin and the solvent is 15 mN/m or more ,
The external electrode paste, wherein the proportion of non-volatile components other than the solvent contained in the external electrode paste is 15 vol % or more and 32 vol % or less . 2. The external electrode paste according to claim 1, wherein the interfacial tension generated between the resin and the solvent is 40 mN/m or more and less than 56 mN/m. 3. The external electrode paste according to claim 1, wherein the Cu filler is particles made of at least one of Cu and a Cu alloy, and has an average particle diameter D50 of 8 μm or less. Claims 1 to 3 , wherein the solvent contains at least one of terpineol, dihydroterpineol, dihydroterpinyl acetate, propylene glycol phenyl ether, benzyl alcohol, texanol, and butyl carbitol acetate. The external electrode paste according to any one of the above.

Images