JP4483799B2 - Manufacturing method of multilayer capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing a multilayer capacitor.

  Conventionally, in the production of multilayer capacitors as disclosed in the following Patent Document 1 and Patent Document 2, a layer made of ceramic dielectric powder constituting a dielectric layer and an internal electrode paste constituting an internal electrode layer A method is adopted in which a laminate in which a plurality of layers are alternately stacked is formed, the laminate is fired, and then external electrodes are provided.

  Here, for the formation of the dielectric layer, a dielectric paste prepared by mixing ceramic dielectric powder, an organic binder, an organic solvent and the like into a slurry is formed into a sheet by a method such as a doctor blade method, and is appropriately dried. A ceramic molded body is used. The internal electrode paste used for forming the internal electrode layer is a paste obtained by dispersing a metal powder such as nickel in an organic binder and an organic solvent. In the above-described laminate, the internal electrode paste is usually screen-printed on the surface of the sheet-like ceramic molded body, the organic solvent contained in the internal electrode paste is dried, and then a plurality of the molded bodies are stacked and pressed. Is produced.

This laminate is made into chips and fired to form a ceramic element. Out of the end faces of the ceramic element, external electrodes are provided on the end faces where the internal electrode layers are exposed, thereby completing the production of the multilayer capacitor.
JP-A-5-190375 Japanese Patent Laid-Open No. 7-211132

  However, when a multilayer capacitor is manufactured using the conventional manufacturing method described above, the breakdown voltage of the obtained multilayer capacitor is smaller than the theoretical breakdown voltage, and the capacitor characteristics are deteriorated due to the occurrence of cracks. Sometimes occurred. As a result of repeated research on these problems, the inventors have newly found a technique that can improve the withstand voltage of the multilayer capacitor and can suppress the occurrence of cracks.

  That is, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a multilayer capacitor in which withstand voltage is improved and cracks are suppressed.

The multilayer capacitor manufacturing method according to the present invention includes a step of applying an electrode paste to a green sheet, a step of drying the electrode paste applied to the green sheet,
There are a step of stacking a plurality of green sheets dried with electrode paste to form a multilayer body, and a step of firing the multilayer body to manufacture a multilayer capacitor in which internal electrode layers and dielectric layers are alternately stacked. The maximum particle size of the conductive powder of the electrode paste is characterized by being in the range of 16% to 60% with respect to the average thickness of the electrode paste after the step of drying the electrode paste.

  The inventors have conducted intensive research and the case where the maximum particle size of the conductive powder of the electrode paste is in the range of 16% to 60% with respect to the average thickness of the electrode paste after the step of drying the electrode paste. In addition, it has been newly found that the withstand voltage of the multilayer capacitor can be improved and the occurrence of cracks can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the multilayer capacitor by which the withstand voltage was improved and the crack was suppressed is provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments that are considered to be the best in carrying out the invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 is a schematic cross-sectional view of a multilayer capacitor according to an embodiment of the present invention. As illustrated in FIG. 1, the multilayer capacitor 10 includes two outermost layers 11, which are outermost layers, approximately 300 dielectric layers 12 sandwiched between the surface layers 11, and dielectric layers 12 disposed above and below. A capacitor element body (ceramic element) 16 having a hexahedral shape having an internal electrode layer 14 interposed therebetween is provided. That is, the capacitor body 16 has a laminated structure of about 600 layers, and the dielectric layers 12 and the internal electrode layers 14 are alternately laminated. Further, of the end faces of the capacitor body 16, a pair of end faces 16 a and 16 b that extend in the thickness direction of the capacitor body 16 and face each other so as to cover the entire area of the end faces 16 a and 16 b. External electrodes 18 and 18 are provided.

  Further, the internal electrode layers 14 arranged above and below are electrically insulated from each other by the dielectric layer 12 and are connected to one external electrode 18 different from each other. Therefore, when a predetermined voltage is applied between the pair of external electrodes 18, 18, electric charges are stored between the internal electrode layers 14 opposed vertically.

Both the surface layer 11 and the dielectric layer 12 are layers mainly composed of BaTiO _3. The thickness of each surface layer 11 is approximately 50 μm, and the thickness of each dielectric layer 12 is approximately 1 to 4 μm. The surface layer 11 and the dielectric layer 12 are formed by firing a green sheet described later. The internal electrode layer 14 is a metal layer containing Ni as a main component and has a thickness of about 1 μm. Each external electrode 18 is a porous body mainly composed of Cu having high conductivity among metals, and the arithmetic average roughness of the surface 18a thereof is about 1 μm.

  Hereinafter, a method for producing the multilayer capacitor 10 described above will be described with reference to FIGS. Here, FIG. 2 is a flowchart showing a procedure for producing the multilayer capacitor 10, FIG. 3 is a process diagram showing the procedure for producing the multilayer capacitor 10, and FIG. 4 shows a printing pattern of the green sheet. It is a partial enlarged view.

In producing the multilayer capacitor 10, first, a BaTiO ₃ -based green sheet 20 is prepared by the following procedure. First, as Step 11 in FIG. 2, BaTiO ₃ powder and an organic binder / organic solvent are mixed to form a slurry. In step 12, the paste obtained by the slurrying is formed into a sheet on a carrier film such as a PET film by using a doctor blade method to produce 300 green sheets 20 having a predetermined thickness. In addition, a green sheet 21 that is thicker than the green sheet 20 and should be the surface layer 11 is also prepared.

In parallel with the production of the green sheets 20 and 21, an electrode paste (internal electrode paste) 22 to be the internal electrode layer 14 is also prepared. This electrode paste 22 is a paste obtained by dispersing Ni powder (conductor powder) in an organic binder and an organic solvent. As the organic binder, known ones can be used. For example, cellulose resin, epoxy resin, aryl resin, acrylic resin, phenol-formaldehyde resin, unsaturated polyester resin, polycarbonate resin, polyamide resin, polyimide resin, alkyd resin, A binder such as rosin ester can be used. Moreover, a well-known thing can be utilized also for an organic solvent, For example, solvents, such as a butyl carbitol, a butyl carbitol acetate, a turpentine oil, (alpha) -TV neol, an ethyl cellosolve, a butyl phthalate, can be used. BaTiO ₃ powder is added to the electrode paste 22 as a co-material. BaTiO ₃ powder for the main component BaTiO ₃ dielectric layer 12 (and the green sheet 20) is the same, the addition of BaTiO ₃ powder to the electrode paste 22, between the electrode paste 22 and green sheet 20 The difference between the shrinkage ratio and the sintering start temperature is significantly relaxed.

  Subsequently, as Step 13 in FIG. 2, an electrode paste 22 having a predetermined pattern is applied to the surface 20a of the green sheet 20 by a screen printing method. More specifically, as shown in FIG. 4, the rectangular region 24 (for example, 1.0 mm × 0.5 mm) corresponding to one multilayer ceramic chip capacitor on the green sheet surface 20a other than the edge region of three sides. The electrode paste 22 is applied to the region.

  Next, as step 14 in FIG. 2, the electrode paste 22 applied to the green sheet 20 is dried under predetermined conditions. As drying conditions for the electrode paste 22, for example, a drying temperature of 60 ° C. to 120 ° C. and a drying time of about 10 minutes are suitable.

  Then, as step 15 in FIG. 2, a plurality of green sheets 20 from which the electrode paste 22 is dried are stacked to form a laminate 26. In order to form the laminated body 26, first, the electrode paste 22 is laminated on the green sheet 21 with the electrode paste 22 facing upward (see FIG. 3A), and then about 300 sheets manufactured using the same method. The green sheets 20 are sequentially laminated so that the positions of the electrode pastes 22 are alternately changed (see FIG. 3B). Finally, an uncoated green sheet 21 is placed on the stacked green sheets 20 and pressed from the stacking direction so that the adjacent green sheets 21, the green sheets 20, and the electrode paste 22 are pressed against each other. Through the above procedure, a laminate 26 in which the green sheets 20 and the electrode pastes 22 are alternately laminated is produced.

  Further, a predetermined binder removal process is performed on the laminated body 26 and the rectangular regions 24 corresponding to one capacitor are cut into chips (see FIG. 3C).

  Thereafter, as step 16 in FIG. 2, the green sheet 21, the green sheet 20, and the electrode paste 22 are respectively fired in a sealed mortar (sheath) at, for example, about 1200 ° C. for 2 hours. The surface layer 11, the dielectric layer 12, and the internal electrode layer 14 described above are formed, and the stacked body 26 is a capacitor body 16 in which the dielectric layers 12 and the internal electrode layers 14 are alternately stacked. Further, surface polishing is performed by processing the capacitor body 16 in a barrel containing water and a polishing medium. This surface polishing may be performed at the stage of the laminated body 26.

  Finally, as step 17 in FIG. 2, an external electrode 18 is formed so as to cover a pair of end faces 16 a and 16 b extending in the laminating direction and facing each other among the end faces of the capacitor body 16. Is completed (see FIG. 3D).

  Here, the electrode paste 22 used for manufacturing the multilayer capacitor 10 will be described in more detail.

  As described above, the electrode paste 22 contains Ni powder as the conductor powder. In the above-described embodiment, the maximum particle size of the Ni powder contained in the electrode paste 22 is based on the average thickness of the electrode paste 22 after the step of drying the electrode paste 22 (ie, step 14). It is adjusted to be within the range of 16% to 60%.

  As a result of intensive studies, the inventors can significantly improve the withstand voltage of the multilayer capacitor 10 to be manufactured by setting the maximum particle size of the Ni powder of the electrode paste 22 in such a range, and It was newly found that the occurrence of cracks can be suppressed.

  It is considered that the above effect is obtained by the following mechanism.

  That is, when the particle size of the Ni powder contained in the electrode paste 22 is small, the shrinkage rate of the electrode paste 22 at the time of main firing (step 16) is high, and is greatly deviated from the shrinkage rate of the green sheet 20. Then, it is considered that cracks occur in the multilayer capacitor 10 because the shrinkage rates between the electrode paste 22 and the green sheet 20 during the main firing are different.

  On the other hand, when the particle size of the Ni powder contained in the electrode paste 22 is large, the thickness of the electrode paste 22 applied to the green sheet 20 is likely to vary, and the surface of the electrode paste 22 is uneven. Therefore, when the electrode paste 22 and the green sheet 20 are pressed when the laminated body 26 is manufactured, the thickness variation of the electrode paste 22 varies due to the unevenness of the surface of the electrode paste 22. Trigger. As a result, it is considered that the dielectric layer 12 has a portion where the layer thickness is partially small, and the withstand voltage of the multilayer capacitor 10 becomes lower than theoretical.

  Therefore, the inventors achieve both improvement of the withstand voltage and suppression of crack generation of the produced multilayer capacitor 10 using the electrode paste 22 in which the maximum particle size of the Ni powder is adjusted to the above-described range. succeeded in.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, the conductor powder is not limited to Ni powder, but may be Ag, Pd, Cu, an Ag—Pd alloy, or the like. Further, the ceramic powder is not limited to BaTiO ₃ powder, but may be (Ba _x Ca _y Sr _1-xy ) (Ti _z Zr _1-z ) O ₃ (for example, CaTiO ₃ or SrTiO ₃ ). Furthermore, the number of stacked elements is not limited to 300 layers, and can be increased or decreased as appropriate.

  Hereinafter, in order to further clarify the effects of the present invention, description will be made using examples.

  Samples # 1 to # 5 used in the examples are samples dried after applying an electrode paste on a green sheet, and were prepared by the same method as in the above-described embodiment. The various dimensions of the sample were an interlayer of 1.0 μm, an internal electrode thickness of 1.0 μm, an outer layer (surface layer) thickness of 30 μm, and external dimensions: length 1.0 mm × width 0.5 mm × height 0.5 mm.

The electrode paste used in this example includes Ni powder as a conductor powder, and was prepared by kneading Ni powder, ceramic powder (co-material), and organic vehicle (ethyl cellulose and terpineol). And after apply | coating this electrode paste on a green sheet, it was made to dry on drying conditions with a drying temperature of 60 to 120 degreeC, and drying time about 10 minutes, and obtained the electrode paste whose average thickness is 1.2 micrometers. The average thickness of the electrode paste is the average value of the thicknesses in the five regions (A1 to A5) of the electrode paste (22) as shown in FIG. 5A, and the thickness of each region is shown in FIG. An intermediate value ((h ₁ + h ₂ ) / 2) between the minimum thickness h ₁ and the maximum thickness h ₂ as shown in FIG.

  Each sample # 1 to # 5 is different only in the maximum particle size of the Ni powder contained in the electrode paste. That is, the maximum particle diameters of the Ni powders of Samples # 1 to # 5 were 0.17 μm, 0.20 μm, 0.50 μm, 0.70 μm, and 0.80 μm, respectively.

  And about each of the said sample, the breakdown voltage (V) and the crack generation rate (ppm) were measured. The measurement results were as shown in the table of FIG.

  From the table shown in FIG. 6, in samples # 2 to # 4 where the value obtained by dividing the Ni powder maximum particle size by the electrode paste average thickness is in the range of 16% to 60%, both the breakdown voltage and the crack generation rate are It was within a range where there was no practical problem. However, in Sample # 1 where the value obtained by dividing the maximum Ni powder particle size by the average electrode paste thickness is smaller than 16%, the crack occurrence rate was very high. Further, in sample # 5 in which the value obtained by dividing the Ni powder maximum particle size by the average electrode paste thickness exceeds 60%, the breakdown voltage was low enough to be unsuitable for practical use.

1 is a schematic cross-sectional view of a multilayer capacitor according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating a procedure for manufacturing the multilayer capacitor illustrated in FIG. 1. FIG. 2 is a process diagram illustrating a procedure for manufacturing the multilayer capacitor illustrated in FIG. 1. It is the elements on larger scale which showed the printing pattern of the green sheet. It is the figure which showed the method of measuring the electrode paste average thickness of the sample which concerns on the Example of this invention. It is the table | surface which showed the measurement result which concerns on the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ceramic capacitor, 11 ... Surface layer, 12 ... Dielectric layer, 14 ... Internal electrode layer, 16 ... Capacitor body, 18 ... External electrode, 18a ... External electrode surface, 20, 21 ... Green sheet, 20a ... Surface, 22 ... electrode paste, 26 ... laminate.

Claims (1)

Preparing an electrode paste;
A step of applying the electrode paste on the green sheet,
Drying the electrode paste applied to the green sheet;
Forming a laminate by stacking a plurality of the green sheets dried with the electrode paste; and
Firing the multilayer body to produce a multilayer capacitor in which internal electrode layers and dielectric layers are alternately stacked, and
In the step of preparing the electrode paste , the maximum particle size of the conductor powder contained in the electrode paste is 16% to 60% with respect to the average thickness of the dried electrode paste after the step of drying the electrode paste. % Is adjusted so that it falls within the range of%.

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