JP7477080B2 - Manufacturing method for ceramic electronic components - Google Patents

Description

The present invention relates to a method for manufacturing ceramic electronic components.

There is an ever-increasing demand for smaller, larger capacity ceramic electronic components such as multilayer ceramic capacitors. In order to achieve larger capacity, it is necessary to make the dielectric layers and internal electrode layers thinner. When trying to make the internal electrode layers thinner, there is a risk that the metal components will become spherical during the firing process, resulting in a decrease in the continuity ratio. Therefore, the decrease in the continuity ratio is suppressed by adding a co-material to the electrode paste (see, for example, Patent Document 1).

JP 2013-254954 A

However, although a sudden decrease in the continuity rate during the firing process is suppressed, there is a risk that the continuity rate will decrease at the end of firing due to the ejection of co-material.

The present invention has been made in consideration of the above problems, and aims to provide a method for manufacturing ceramic electronic components that can suppress a decrease in the continuity ratio of the internal electrode layers.

The method for manufacturing ceramic electronic components according to the present invention is characterized by comprising the steps of forming a laminate by stacking a plurality of lamination units, each of which has a pattern of a metal conductive paste arranged on a dielectric green sheet containing ceramic powder, such that the arrangement of the metal conductive paste is shifted alternately, and firing the laminate while applying pressure by a pressure means in the lamination direction of the dielectric green sheet.

In the method for manufacturing the ceramic electronic component, the laminate may be fired while applying a pressure of 0.05 MPa or more and 1.5 MPa or less in the stacking direction of the dielectric green sheets by the pressure means.

In the method for manufacturing a ceramic electronic component, in the step of firing the laminate, pressure may be applied by the pressurizing means after the temperature of the firing atmosphere reaches 800°C or higher.

In the method for manufacturing ceramic electronic components, the amount of co-material added to the metal conductive paste may be 0.1 parts or less.

In the method for manufacturing the ceramic electronic component, the average thickness of the internal electrode layer obtained by firing the metal conductive paste may be 0.5 μm or less.

The present invention provides a method for manufacturing ceramic electronic components that can suppress a decrease in the continuity ratio of the internal electrode layers.

FIG. 2 is a partial cross-sectional perspective view of a multilayer ceramic capacitor. FIG. 13 is a diagram showing a continuity ratio. 1 is a diagram illustrating a flow of a method for manufacturing a multilayer ceramic capacitor. 13A and 13B are diagrams illustrating examples of pressure directions.

The following describes the embodiment with reference to the drawings.

(Embodiment)
Fig. 1 is a partial cross-sectional perspective view of a multilayer ceramic capacitor 100 according to an embodiment. As illustrated in Fig. 1, the multilayer ceramic capacitor 100 includes a laminated chip 10 having a rectangular parallelepiped shape, and external electrodes 20a, 20b provided on two opposing end faces of the laminated chip 10. Of the four faces of the laminated chip 10 other than the two end faces, the two faces other than the top and bottom faces in the stacking direction are referred to as side faces. The external electrodes 20a, 20b extend on the top, bottom and two side faces in the stacking direction of the laminated chip 10. However, the external electrodes 20a, 20b are spaced apart from each other.

The laminated chip 10 has a configuration in which dielectric layers 11, mainly made of a ceramic material that functions as a dielectric, and internal electrode layers 12, mainly made of a metal material such as a base metal material, are alternately laminated. The edges of each internal electrode layer 12 are alternately exposed to the end face of the laminated chip 10 on which the external electrode 20a is provided and the end face on which the external electrode 20b is provided. As a result, each internal electrode layer 12 is alternately conductive to the external electrode 20a and the external electrode 20b. As a result, the laminated ceramic capacitor 100 has a configuration in which multiple dielectric layers 11 are laminated via the internal electrode layers 12. In addition, in the laminated structure of the dielectric layers 11 and the internal electrode layers 12, the internal electrode layers 12 are arranged on the outermost layer in the lamination direction, and the upper and lower surfaces of the laminated structure are covered by the cover layer 13. The cover layer 13 is mainly made of a ceramic material. For example, the material of the cover layer 13 has the same main component ceramic material as that of the dielectric layers 11.

The size of the multilayer ceramic capacitor 100 is, for example, 0.25 mm long, 0.125 mm wide, and 0.125 mm high, or 0.4 mm long, 0.2 mm wide, and 0.2 mm high, or 0.6 mm long, 0.3 mm wide, and 0.3 mm high, or 1.0 mm long, 0.5 mm wide, and 0.5 mm high, or 3.2 mm long, 1.6 mm wide, and 1.6 mm high, or 4.5 mm long, 3.2 mm wide, and 2.5 mm high, but is not limited to these sizes.

The internal electrode layer 12 is mainly composed of a base metal such as Ni (nickel), Cu (copper), or Sn (tin). The internal electrode layer 12 may be mainly composed of a precious metal such as Pt (platinum), Pd (palladium), Ag (silver), or Au (gold), or an alloy containing these. The average thickness of the internal electrode layer 12 is, for example, 0.5 μm or less, and preferably 0.3 μm or less. The dielectric layer 11 is mainly composed of a ceramic material having a perovskite structure represented by the general formula ABO _3. The perovskite structure includes ABO _3-α , which is deviated from the stoichiometric composition. For example, the ceramic material may be _BaTiO3 (barium titanate), _CaZrO3 (calcium zirconate), _CaTiO3 (calcium titanate), _SrTiO3 (strontium titanate), _or Ba1 _-x- yCaxSryTi1 _{- zZrzO3} (0≦x≦1, 0≦y≦ ₁ , 0≦z≦1) which forms a _perovskite structure.

When the internal electrode layer 12 is obtained by sintering metal powder, it becomes spherical as sintering progresses in order to minimize the surface energy. Since the metal component of the internal electrode layer 12 sinters more easily than the main ceramic component of the dielectric layer 11, if the temperature is raised until the main ceramic component of the dielectric layer 11 sinters, the metal component of the internal electrode layer 12 becomes oversintered and tries to become spherical. In this case, if there is a break (defect), the internal electrode layer 12 will break from the defect as a base point, and the continuity rate will decrease. If the continuity rate of the internal electrode layer 12 decreases, the capacity of the multilayer ceramic capacitor 100 will decrease.

Figure 2 is a diagram showing the continuity ratio. As shown in the example of Figure 2, in an observation area of length L0 in a certain internal electrode layer 12, the lengths L1, L2, ..., Ln of the metal parts are measured and summed, and the ratio of the metal parts, ΣLn/L0, can be defined as the continuity ratio of that layer. A decrease in the continuity ratio is particularly likely to occur in thin-layered multilayer ceramic capacitors 100 in which the average thickness of the internal electrode layers 12 is 0.5 μm or less.

In this embodiment, a method for manufacturing a multilayer ceramic capacitor 100 that can suppress a decrease in the continuity rate of the internal electrode layers 12 is described. Figure 3 is a diagram illustrating the flow of the method for manufacturing a multilayer ceramic capacitor 100.

(Raw material powder preparation process)
First, a dielectric material for forming the dielectric layer 11 is prepared. The A-site elements and B-site elements contained in the dielectric layer 11 are usually contained in the dielectric layer 11 in the form of a sintered body of _ABO3 particles. For example, _BaTiO3 is a tetragonal compound having a perovskite structure and exhibits a high dielectric constant. This _BaTiO3 can generally be obtained by synthesizing barium titanate by reacting a titanium raw material such as titanium dioxide with a barium raw material such as barium carbonate. Various methods have been known so far as a method for synthesizing the ceramics constituting the dielectric layer 11, such as a solid-phase method, a sol-gel method, a hydrothermal method, and the like. In this embodiment, any of these methods can be adopted.

To the obtained ceramic powder, a specific additive compound is added according to the purpose. Examples of additive compounds include oxides of Mo (molybdenum), Nb (niobium), Ta (tantalum), W (tungsten), Mg (magnesium), Mn (manganese), V (vanadium), Cr (chromium), rare earth elements (Y (yttrium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), and Yb (ytterbium)), as well as oxides or glasses of Co (cobalt), Ni, Li (lithium), B (boron), Na (sodium), K (potassium), and Si.

In this embodiment, preferably, first, a compound containing an additive compound is mixed with the ceramic particles constituting the dielectric layer 11, and calcined at 820 to 1150°C. The resulting ceramic particles are then wet-mixed with the additive compound, dried, and pulverized to prepare a ceramic powder. For example, the average particle size of the ceramic powder is preferably 50 to 300 nm from the viewpoint of thinning the dielectric layer 11. For example, the ceramic powder obtained as described above may be pulverized as necessary to adjust the particle size, or may be combined with a classification process to adjust the particle size.

(Lamination process)
Next, a binder such as polyvinyl butyral (PVB) resin, an organic solvent such as ethanol or toluene, and a plasticizer are added to the obtained dielectric material and wet mixed. Using the obtained slurry, a dielectric green sheet is applied onto a substrate by, for example, a die coater method or a doctor blade method, and then dried.

Next, a metal conductive paste for forming an internal electrode containing an organic binder is printed on the surface of the dielectric green sheet by screen printing, gravure printing, or the like to arrange a pattern for the internal electrode layer. Ceramic particles may or may not be added to the metal conductive paste as a co-material. When ceramic particles are added as a co-material, the main component of the ceramic particles is not particularly limited, but is preferably the same as the main ceramic component of the dielectric layer 11.

After that, in a state where it is peeled off from the substrate, the dielectric green sheets are alternately stacked so that the internal electrode layers 12 and the dielectric layers 11 are alternately arranged, and so that the edges of the internal electrode layers 12 are alternately exposed at both longitudinal end faces of the dielectric layers 11 and alternately drawn out to a pair of external electrodes 20a, 20b of different polarity. For example, the total number of layers is 100 to 500 layers. Then, a ceramic laminate is obtained by pressing a plurality of cover sheets that become the cover layers 13 onto the top and bottom of the laminate of the stacked dielectric green sheets. The obtained ceramic laminate is then cut to a predetermined chip size (for example, 1.0 mm x 0.5 mm).

(Firing process)
As shown in Fig. 4(a), the molded body 41 thus obtained is subjected to a binder removal process in a _N2 atmosphere, and then a metal paste 42 that will become the base of the external electrodes 20a, 20b is applied by dipping, and the body is fired at 1100 to 1300°C for 10 minutes to 2 hours in a reducing atmosphere with an oxygen partial pressure of ^10-5 to ^10-8 atm. In Fig. 4(a), the up-down direction is the lamination direction of the dielectric green sheets. The same is true for Fig. 4(b).

During this firing process, pressure is applied in the lamination direction of the dielectric green sheets by a pressure means. For example, the molded body 41 is placed on a pedestal, and pressure is applied to the molded body 41 by a plate carrying a weight, etc., to pressurize the molded body 41 in one axial direction in the lamination direction of the dielectric green sheets. Therefore, pressure is applied to the molded body 41 so that it exceeds the atmospheric pressure applied to the molded body 41. In this case, the movement of the metal conductive paste for forming the internal electrodes in the in-plane direction is suppressed, and the spherical shape of the internal electrode layer 12 is suppressed. This suppresses a decrease in the continuity rate of the internal electrode layer 12.

As shown in FIG. 4(b), the atmosphere surrounding the molded body 41 may be pressurized to a pressure higher than atmospheric pressure so that the entire molded body 41 is pressurized. That is, gas pressurization may be used. For example, the atmospheric pressure can be increased by using a gas pump. Even in this case, pressure is applied in the stacking direction of the dielectric green sheets, so that the in-plane movement of the metal conductive paste for forming the internal electrodes is suppressed, and the internal electrode layer 12 is suppressed from becoming spherical.

(Reoxidation treatment process)
Thereafter, a re-oxidation treatment may be performed at 600° C. to 1000° C. in a N ₂ gas atmosphere.

(Plating process)
Thereafter, the external electrodes 20a, 20b may be coated with a metal such as Cu, Ni, Sn, etc. by electrolytic plating or the like.

According to the method for manufacturing a multilayer ceramic capacitor according to this embodiment, the firing process is performed while pressure is applied to the molded body 41 by the pressure means in the lamination direction of the dielectric green sheets, so that the movement of the metal conductive paste for forming the internal electrodes in the in-plane direction is suppressed, and the internal electrode layers 12 are suppressed from becoming spherical. This suppresses a decrease in the continuity rate of the internal electrode layers 12.

If the pressure in the lamination direction of the dielectric green sheets is too small, the internal electrode layer 12 may not be sufficiently suppressed from becoming spherical. Therefore, it is preferable to set a lower limit for the pressure. For example, in addition to atmospheric pressure, it is preferable to apply a pressure of 0.05 MPa or more by the pressure means in the lamination direction of the dielectric green sheets, and it is more preferable to apply a pressure of 0.15 MPa or more. On the other hand, if the pressure is too large, the components of the dielectric layer 11 and the components of the internal electrode layer 12 may diffuse into each other. Therefore, it is preferable to set an upper limit for the pressure. For example, in addition to atmospheric pressure, it is preferable to apply a pressure of 1.5 MPa or less by the pressure means in the lamination direction of the dielectric green sheets, and it is more preferable to apply a pressure of 1.0 MPa or less.

According to the manufacturing method of this embodiment, the decrease in the continuity of the internal electrode layer 12 can be suppressed without adding a common material to the metal conductive paste for forming the internal electrode. The common material generally has a small diameter, so if it is discharged into the dielectric layer 11, it may reduce the dielectric constant of the dielectric layer 11. Therefore, it is preferable to reduce the amount of the common material added to the metal conductive paste. For example, it is preferable to set the amount of the common material added to the metal weight in the metal conductive paste to 0.1 parts or less, and it is more preferable to add no common material. In this case, the amount of the common material discharged into the dielectric layer 11 during the firing process is reduced or eliminated, so that the decrease in the dielectric constant of the dielectric layer 11 can be suppressed.

The internal electrode layer 12 begins to be spheroidized after it has reached a high temperature. Therefore, the pressurizing means may start applying pressure after the temperature of the firing atmosphere has reached a predetermined temperature or higher. For example, when the main component metal of the internal electrode layer 12 is Ni, it is preferable to start applying pressure by the pressurizing means after the temperature of the firing atmosphere has reached 800°C or higher. For example, when increasing the pressure of the atmosphere surrounding the molded body 41, the decrease in binder removal efficiency can be suppressed by not applying pressure until halfway through the temperature rise.

In the above embodiments, a multilayer ceramic capacitor has been described as an example of a ceramic electronic component, but the present invention is not limited to this. For example, other electronic components such as a varistor or a thermistor may be used.

The multilayer ceramic capacitor according to the embodiment was fabricated and its characteristics were investigated.

Example 1
Necessary additives were added to the barium titanate powder, and the mixture was thoroughly wet-mixed and pulverized in a ball mill to obtain a dielectric material. An organic binder and a solvent were added to the dielectric material, and a dielectric green sheet was prepared by the doctor blade method. Polyvinyl butyral (PVB) or the like was used as the organic binder, and ethanol, toluene, or the like was added as the solvent. In addition, a plasticizer or the like was added. Next, a metal conductive paste for forming an internal electrode was prepared, which contains a powder of the main component metal of the internal electrode layer 12, a binder, a solvent, and other auxiliary agents as necessary. No co-material was added. The organic binder and solvent of the metal conductive paste were different from those of the dielectric green sheet. The metal conductive paste for forming the internal electrode was screen-printed on the dielectric sheet. The dielectric green sheet on which the metal conductive paste for forming the internal electrode was printed was overlapped. A plurality of cover sheets were laminated on the top and bottom of the obtained laminate. Then, a ceramic laminate was obtained by thermocompression bonding, and cut into a predetermined shape.

The obtained molded body 41 was debindered in a _N2 atmosphere, and then a metal paste 42 containing a metal filler mainly composed of Ni, a common material, a binder, and a solvent was applied to both end faces of the molded body 41 and the top, bottom, and each side in the stacking direction, and then dried. The metal paste was then fired simultaneously with the molded body 41 at 1100°C to 1300°C in a reducing atmosphere for 10 minutes to 2 hours to obtain a sintered body. During this firing process, a pressure of 0.05 MPa in addition to atmospheric pressure was applied by a plate in the stacking direction of the dielectric green sheets.

The sintered body was subjected to a reoxidation treatment under the condition of 800°C in a _N2 atmosphere, and then a plating treatment was performed to form a Cu plating layer, a Ni plating layer and a Sn plating layer on the surfaces of the external electrodes 20a, 20b, thereby obtaining a multilayer ceramic capacitor 100. The shape dimensions of the obtained multilayer ceramic capacitor 100 were length 1.0 mm x width 0.5 mm x height 0.5 mm.

Example 2
The conditions were the same as in Example 1, except that 5 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

Example 3
The conditions were the same as in Example 1, except that 10 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

Example 4
The conditions were the same as in Example 1, except that 15 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

Example 5
The conditions were the same as in Example 1, except that 20 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

(Comparative Example 1)
The conditions were the same as in Example 1, except that no pressure was applied by the pressurizing means during the firing process.

(Comparative Example 2)
The conditions were the same as those of Comparative Example 1, except that 5 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

(Comparative Example 3)
The conditions were the same as those of Comparative Example 1, except that 10 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

(Comparative Example 4)
The conditions were the same as those of Comparative Example 1, except that 15 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

(Comparative Example 5)
The conditions were the same as those of Comparative Example 1, except that 20 parts of barium titanate was added to the metal conductive paste for forming the internal electrodes.

(analysis)
The continuity ratio of the internal electrode layer 12 in Examples 1 to 5 and Comparative Examples 1 to 5 was measured. For the measurement, a SEM (scanning electron microscope) photograph of a cross section in the lamination direction of the dielectric layer 11 and the internal electrode layer 12 at the center of the chip was used. Specifically, the continuity ratios of all the internal electrode layers shown in several SEM photographs were measured, and the average value was calculated as the continuity ratio. The capacitance was measured under conditions of 1 kHz and 0.5 Vrms. Regarding the capacitance, when the reduction was within 10% of the calculated capacitance calculated from the material dielectric constant, the dielectric layer thickness, the number of layers, and the electrode area, it was judged as very good "◯", when the reduction was within 10 to 20%, it was judged as good "△", and when the reduction was more than 20%, it was judged as poor "X".

Table 1 shows the results of the measured continuity ratio and capacity. As shown in Table 1, the continuity ratio is high in all of Examples 1 to 5. In addition, when Examples 1 to 5 are compared with Comparative Examples 1 to 5, if the amount of the co-material added is the same, the continuity ratio is higher in Examples 1 to 5. This is thought to be because sintering was performed while applying pressure by a pressure means in the lamination direction of the dielectric green sheets, thereby suppressing the spheroidization of the internal electrode layers 12.

As shown in Table 1, the capacitance was judged to be good (△) or very good (◯) in Examples 1 to 5. This is believed to be because the continuity rate of the internal electrode layer 12 was increased. The judgment results for Examples 1 to 3 were good compared to the judgment results for Examples 4 and 5. This is believed to be because the amount of common material added was reduced, reducing the amount of common material discharged into the dielectric layer 11 and suppressing the decrease in the dielectric constant of the dielectric layer 11.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 10 laminated chip 11 dielectric layer 12 internal electrode layer 13 cover layer 20a, 20b external electrode 100 laminated ceramic capacitor

Claims (6)

forming a laminate by laminating a plurality of lamination units, each lamination unit having a pattern of a metal conductive paste arranged on a dielectric green sheet containing ceramic powder, such that the arrangement of the metal conductive paste is shifted alternately;
and firing the laminate while pressurizing the atmosphere surrounding the laminate to a pressure higher than atmospheric pressure so that the entire laminate is pressurized.
A method for producing a ceramic electronic component , wherein in the step of firing the laminate, after the temperature of the firing atmosphere has reached 800° C. or higher, the surrounding atmosphere is pressurized with gas so that the pressure exceeds atmospheric pressure. 2. The method for producing a ceramic electronic component according to claim 1, wherein the laminate is fired while applying a pressure of 0.05 MPa or more and 1.5 MPa or less in a lamination direction of the dielectric green sheets. 3. The method for producing a ceramic electronic component according to claim 1, wherein the amount of the co-material added to the metal conductive paste is 0.1 part or less. 4. The method for producing a ceramic electronic component according to claim 1, wherein an average thickness of an internal electrode layer obtained by firing the metal conductive paste is 0.5 μm or less. 5. The method for producing a ceramic electronic component according to claim 1, wherein the metal conductive paste contains ceramic particles and metal powder as co-materials. The method for producing a ceramic electronic component according to any one of claims 1 to 4 , wherein the metal conductive paste does not contain a co-material.

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