JP2009266716A - Conductive paste, and manufacturing method of laminated ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste capable of preventing drop of capacitance by internal electrode breakage, and hardly causing a short failure; and a manufacturing method of a laminated ceramic capacitor. <P>SOLUTION: In this conductive paste, nickel powder 21 is coated with ceramic powder 22 adhering to surfaces of particles thereof, and its coverage factor is ≥50%; the internal electrode breakage can be thereby prevented even when it is formed into a thin layer by a sintering delay effect of the nickel powder by the ceramic powder; and a thin, flat and continuous internal electrode can be formed. This manufacturing method of a laminated ceramic capacitor using the conductive paste can manufacture, with a high yield, the laminated ceramic capacitor that can prevent drop of capacitance by the internal electrode breakage even when the internal electrode and a dielectric layer are each formed into the thin layer, is large in obtained capacitance and hardly causes a short failure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a conductive paste used for, for example, a multilayer ceramic capacitor, and a method for manufacturing a multilayer ceramic capacitor using the same.

  2. Description of the Related Art In recent years, multilayer ceramic capacitors, which are typical multilayer ceramic electronic components, have been made thinner and higher in internal electrodes and dielectric layers in order to reduce the size and increase the capacity. For example, in a multilayer ceramic capacitor, both internal electrodes and dielectric layers having a thickness of about 1.0 μm or less are being put to practical use.

  In order to reduce the thickness and increase the number of multilayer ceramic capacitors, it is an important issue to reduce the thickness of the internal electrodes. In order to reduce the thickness of the internal electrode, it is necessary to reduce the thickness of the conductive paste film after drying that becomes the internal electrode. However, when the conductive paste film is thinned, generally, the metal powder in the conductive paste film serving as the internal electrode is sintered faster than the dielectric ceramic sheet. Occurrence of structural defects due to differences in shrinkage behavior at the time of sintering, or if the internal electrode is sintered too much, the continuity of the internal electrode is reduced, causing problems such as a decrease in capacitance due to so-called internal electrode breakage. To do.

  In order to prevent these problems, a method of adding a ceramic material called a co-material to the conductive paste in addition to the metal powder that becomes the internal electrode, for example, nickel powder, and delaying the sintering of the nickel powder that becomes the internal electrode Has been adopted. As the ceramic material used as the co-material, a material having the same composition as the ceramic powder contained in the dielectric ceramic sheet or a material having the main component of the ceramic powder is used.

For example, Patent Document 1 and Patent Document 2 are known as prior art document information related to the invention of this application.
JP 2001-110233 A JP 2000-277369 A

  However, even in the above-described conventional method, in order to reduce the thickness of the internal electrode to about 1.0 μm or less, when the conductive paste film after drying that becomes the internal electrode is thinned, the conductive paste Since the amount of metal powder in the film is small, internal electrode breakage due to oversintering of the metal powder that becomes the internal electrode is likely to occur, the capacitance decreases and the variation becomes large, and the desired capacitance can be obtained. There is no problem. Furthermore, since the internal electrode is locally thickened by oversintering of the metal powder used as the internal electrode, the dielectric layer is reduced in the case of a multilayer ceramic capacitor with a thin dielectric layer and a large number of layers. There is a problem that the internal electrode breaks through and short-circuit defects are likely to occur.

  SUMMARY OF THE INVENTION The present invention solves the above-described problem. Even when the internal electrode and the dielectric layer are thinned, the capacitance of the internal paste and the multilayer ceramic capacitor can be prevented from decreasing due to the internal electrode shortage and the short-circuit failure is reduced. The object is to provide a manufacturing method.

  In order to achieve the above object, the conductive paste of the present invention is a conductive paste containing nickel powder, ceramic powder, an organic binder, and a solvent, and the nickel powder is coated with the ceramic powder adhered to the particle surface. The coverage is 50% or more.

  The method for producing a multilayer ceramic capacitor according to the present invention includes a first step of producing a dielectric ceramic sheet containing a dielectric ceramic powder and an organic binder, and a step of forming a conductive paste film using a conductive paste. A third step of laminating the dielectric ceramic sheet and the conductive paste film to produce a laminate, and a fourth step of firing the laminate to produce a sintered body, The conductive paste includes nickel powder, ceramic powder, an organic binder, and a solvent, and the nickel powder is coated with the ceramic powder attached to the particle surface, It is set as the structure using what has a coverage of 50% or more.

  According to the conductive paste of the present invention, due to the above-described configuration, the internal electrode breakage can be prevented even when thinned due to the sintering delay effect of the nickel powder by the ceramic powder during firing. A continuous internal electrode can be formed.

  In addition, according to the method for manufacturing a multilayer ceramic capacitor of the present invention, even when the internal electrode and the dielectric layer are thinned, the electrostatic capacity can be prevented from being lowered due to the internal electrode being cut off, and the obtained static electricity can be obtained. Large electric capacity and few short circuit defects. In addition, it is possible to manufacture a high-quality and highly reliable multilayer ceramic capacitor with a high yield without occurrence of structural defects or thermal cracks.

(Embodiment)
Hereinafter, a conductive paste of the present invention and a method for manufacturing a multilayer ceramic capacitor using the same will be described in detail using an embodiment.

  First, a dielectric ceramic sheet having a thickness of 2 μm is obtained by forming a slurry obtained by adding a solvent and an organic binder to a dielectric ceramic powder containing barium titanate as a main component and mixing them, by a method such as a doctor blade method.

  On the other hand, the conductive paste in the present embodiment is produced as follows. Three types of nickel powders having an average particle diameter of 0.2 μm, 0.4 μm, and 0.5 μm by observation with a scanning electron microscope are prepared, and a solvent and an organic binder are added to each of these nickel powders, and the mixture is kneaded to obtain nickel. Make a paste. In addition, two kinds of barium titanate powders having an average particle diameter of 0.05 μm and 0.1 μm by observation with a scanning electron microscope were prepared as the co-material ceramic powder, and each of these barium titanate powders was treated with an organic solvent. A vehicle paste that is uniformly dispersed therein and added with a vehicle containing a binder is then kneaded to produce a co-material paste. Next, various combinations of the above-mentioned nickel paste and co-material paste are added, and the co-material paste is added to the nickel paste so that the weight of the barium titanate powder is 20% of the weight of the nickel powder. By kneading and dispersing, eight types of conductive pastes of sample numbers 1 to 8 shown in (Table 1) were obtained. Sample Nos. 1, 3, 4, 6, and 7 repeat the dispersion with three rolls five times in order to increase the coverage of the barium titanate ceramic powder adhering to and covering the nickel powder. It was. In contrast, Sample Nos. 2, 5, and 8 used as comparative examples were dispersed only once with three rolls.

Subsequently, using each of the conductive pastes of Sample Nos. 1 to 8 in (Table 1), a coating amount of 0.5 mg / cm ² of nickel powder was applied on the above dielectric ceramic sheet in a predetermined pattern by screen printing. Eight types of dielectric ceramic sheets on which a conductive paste film serving as an internal electrode was formed were printed. Note that the size, shape, and arrangement of the conductive paste film serving as the internal electrode of the predetermined pattern were set so that an individual monolithic ceramic capacitor could be obtained when cut and separated in a later step. The amount of nickel powder applied was measured by a fluorescent X-ray measurement method. The thickness of the conductive paste film was 1.2 to 1.3 μm.

  And about the dielectric ceramic sheet | seat in which these 8 types of conductive paste films | membranes were formed, a conductive paste film | membrane was observed using a scanning electron microscope, and the ceramic powder of barium titanate as a co-material adhered to nickel powder. The coated state was evaluated.

  Evaluation of the coating state of the nickel powder with the ceramic powder at this time, as shown in FIG. 1 and FIG. 2, when viewed in plan from one direction, that is, in the hemispherical portion of the nickel powder 21, the barium titanate ceramic powder 22 When the area of the maximum part 23 of the part which is not covered at all is less than 50% of the area of the hemispherical part, the nickel powder having a covering rate of 50% or more is used. On the contrary, as shown in FIGS. In addition, in the hemispherical portion of the nickel powder 21, when the area of the maximum portion 23 of the portion not covered at all by the barium titanate ceramic powder 22 is 50% or more of the area of the hemispherical portion, the coverage is 50%. Less than nickel powder. Then, using a scanning electron microscope, 10 fields of view are observed in the field of 5 times and 10 times the average particle diameter of the nickel powder 21, and the nickel powder 21 with a coverage of less than 50% by the ceramic powder 22 is 1 When one was present, the conductive paste was evaluated as a conductive paste having a coverage of less than 50%. When none was present, the conductive paste was evaluated as a conductive paste having a coverage of 50% or more. The evaluation results are also shown in (Table 1).

  Next, using the dielectric ceramic sheets formed with the eight types of conductive paste films prepared above, for each, 170 dielectric ceramic sheets formed with conductive paste films were alternately shifted and laminated, A plurality of dielectric ceramic sheets without a conductive paste film were laminated as protective layers above and below to obtain a laminate. The obtained laminate was subjected to thermocompression bonding to form a laminate block, and then cut and separated into a predetermined shape to obtain individual laminates. Thereafter, the stack of individual pieces was heat-treated to remove the binder, and then fired at a maximum temperature of 1250 ° C. in a non-oxidizing atmosphere of nickel to obtain a sintered body. Copper paste is applied to both end faces where the internal electrode of the obtained sintered body is exposed and baked at 900 ° C. in an industrial nitrogen atmosphere, and then Ni plating and Sn plating are performed to form the external electrode Then, 8 types of multilayer ceramic capacitors of sample numbers 11 to 18 shown in Table 2 using the above-described 8 types of conductive paste were produced.

  The eight types of multilayer ceramic capacitors thus produced were the same in design specifications except for the conductive paste used, that is, the material, thickness and number of layers of the dielectric ceramic sheet, and the conductor layer pattern serving as the internal electrode And the target capacitance was 1.0 μF ± 10%. In addition, the outer dimensions of the multilayer ceramic capacitor were 1.0 mm in length, 0.5 mm in width, and 0.5 mm in thickness.

  The eight types of multilayer ceramic capacitors produced as described above were evaluated for electrical characteristics, presence or absence of sintered body structural defects, and thermal shock resistance. The evaluation results are shown in (Table 2).

  In addition, the electrical characteristics evaluated the electrostatic capacitance and the short circuit defect about 100 samples. The capacitance was measured using an LCR meter at a frequency of 1 kHz and a measurement voltage of 1 Vrms, and the average value was obtained. The short-circuit defect was defined as the number of short-circuit defects by counting those that could not be applied with the measurement voltage of 1 Vrms as short-circuit defects when measuring the capacitance.

  In addition, the presence or absence of a sintered body structural defect was observed for each of 5000 samples using a metal microscope, and the number of defects such as cracks and cracks on the surface of the sintered body was counted to determine the number of structural defect defects. The thermal shock resistance of each of 100 samples was impregnated in a solder bath at 330 ° C. for 5 seconds and taken out, and then observed using a metal microscope to check for the occurrence of thermal cracks due to thermal shock. The number of occurrences was examined.

  As is clear from the evaluation results of (Table 2), Sample No. 12 (Sample No. 2 of the conductive paste used), Sample in which the conductive paste used has a nickel powder coverage of less than 50% with ceramic powder. Each of the multilayer ceramic capacitors of Comparative Example No. 15 (Sample No. 5 of the conductive paste used) and Sample No. 18 (Sample No. 8 of the conductive paste used) has a capacitance of less than 0.9 pF. The target capacitance is smaller than 1.0 μF ± 10%, the number of short-circuit defects and the number of structural defects are large, and thermal cracks are generated, and the target product is not obtained.

  As described above, when the coverage of the nickel powder by the ceramic powder is less than 50%, the sintering delay effect of the nickel powder by the ceramic powder cannot be sufficiently obtained during firing, Since the continuity of the internal electrode is impaired and a portion where the internal electrode is locally thick is generated, the capacitance is small and a number of short-circuit defects are generated. In addition, there is a large difference in shrinkage behavior during sintering between the internal electrode and the dielectric ceramic, and strain is likely to remain inside the multilayer ceramic capacitor after sintering, resulting in structural defects and thermal shock resistance. Thermal cracks have also occurred in the test.

  In contrast, Sample No. 11 (Sample No. 1 of the used conductive paste) and Sample No. 13 (Used conductive paste) in which the conductive paste used had a nickel powder coverage of 50% or more with ceramic powder. Sample number 3), sample number 14 (sample number 4 of the conductive paste used), sample number 16 (sample number 6 of the conductive paste used) and sample number 17 (sample number 7 of the conductive paste used). Each of the multilayer ceramic capacitors according to the manufacturing method of the present invention has a capacitance of 0.9 pF or more and a target capacitance of 1.0 μF ± 10% is obtained, and the number of short-circuit defects is small. Neither structural defects nor thermal cracks occurred, and the target product was obtained.

  And about the laminated ceramic capacitor by the manufacturing method of this invention of said sample number 11, 13, 14, 16 and 17, the cross section was observed with the scanning electron microscope, As a result, thickness was 0.9-1.0 micrometer and it was continuous. It was confirmed that this was a flat internal electrode.

  In particular, sample numbers 13, 14, and 6 using the conductive pastes of the present invention of sample numbers 3, 4, 6 and 7 having a coverage of 50% or more and an average particle diameter of nickel powder of 0.4 μm or less. In the multilayer ceramic capacitors 16 and 17 according to the manufacturing method of the present invention, the capacitance is 0.95 pF or more, the target capacitance is 1.0 μF ± 10%, and the yield is high. The number was even smaller, and the target product could be manufactured with extremely high yield.

  As mentioned above, when the conductive paste used has a nickel powder coverage of 50% or more with ceramic powder, the internal electrode is prevented from being cut off due to the sintering delay effect of the nickel powder with ceramic powder during firing. A thin, flat and continuous internal electrode can be formed. Thereby, the obtained electrostatic capacitance is large, and a thin and flat internal electrode can be formed. Therefore, the dielectric ceramic sheet is not pierced, so that there is little short-circuit defect. In addition, since the sintering of the internal electrode is closer to the sintering of the dielectric ceramic, it is difficult for distortion to remain in the sintered ceramic capacitor after sintering, and there is no occurrence of structural defects or thermal cracks. A multilayer ceramic capacitor with high quality and reliability can be obtained.

  As described above, the conductive paste of the present invention is coated with ceramic powder having nickel powder adhered to the particle surface, and the coverage is 50% or more. Due to the sintering delay effect of the nickel powder, the internal electrode can be prevented from being cut even when the layer is thinned, and a thin, flat and continuous internal electrode can be formed. And the manufacturing method of the multilayer ceramic capacitor of the present invention uses the above-mentioned conductive paste. Thereby, even when the internal electrode and the dielectric layer are thinned, the capacitance is reduced due to the internal electrode being cut. Can be prevented, the capacitance obtained is large, and there are few short-circuit defects. In addition, it is possible to manufacture a high-quality and highly reliable multilayer ceramic capacitor with a high yield without occurrence of structural defects or thermal cracks.

  In the present embodiment, in order to show as a comparative example, an example in which a multilayer ceramic capacitor was manufactured using a conductive paste having a nickel powder coverage of less than 50% was shown. In the production of the multilayer ceramic capacitor, the conductive paste is observed and evaluated by the above-described method prior to the use of the conductive paste. The nickel powder is coated with the ceramic powder adhered to the particle surface, and the coverage is 50%. It is preferable to select and use the above conductive paste. Thereby, manufacturing loss can be avoided.

  In the present embodiment, an example in which only barium titanate powder is used as the co-material ceramic powder has been described. However, the ceramic powder having the same composition as the ceramic powder contained in the dielectric ceramic sheet, or the dielectric ceramic sheet The same effect can be obtained by using the material composition of the main component of the ceramic powder.

  The conductive paste according to the present invention can prevent the internal electrode from being cut even when it is thinned, and a thin, flat and continuous internal electrode can be formed. The method for manufacturing a multilayer ceramic capacitor according to the present invention can prevent a decrease in capacitance due to internal electrode shortage even when the internal electrode and the dielectric layer are thinned. Therefore, it is particularly useful as a method for manufacturing a multilayer ceramic capacitor in which a thin layer and a high multilayer are required.

Schematic external view showing an example of nickel powder with a ceramic powder coverage of 50% or more Schematic external view showing another example of nickel powder with a ceramic powder coverage of 50% or more Schematic external view showing an example of nickel powder with a ceramic powder coverage of less than 50% Schematic external view showing another example of nickel powder with a ceramic powder coverage of less than 50%

Explanation of symbols

21 Nickel powder 22 Ceramic powder 23 Maximum part of uncoated part

Claims (4)

A conductive paste comprising nickel powder, ceramic powder, an organic binder, and a solvent, wherein the nickel powder is coated with the ceramic powder adhered to the particle surface, and the coverage is 50% or more. The conductive paste according to claim 1, wherein the average particle diameter of the nickel powder is 0.4 μm or less. A first step of producing a dielectric ceramic sheet containing a dielectric ceramic powder and an organic binder, a second step of forming a conductive paste film using a conductive paste, the dielectric ceramic sheet and the conductive material A method for producing a multilayer ceramic capacitor comprising: a third step of laminating a conductive paste film to produce a laminated body; and a fourth step of firing the laminated body to produce a sintered body, The conductive paste includes a nickel powder, a ceramic powder, an organic binder, and a solvent, and the nickel powder is coated with the ceramic powder adhered to the particle surface, and a multilayer ceramic using a covering ratio of 50% or more Capacitor manufacturing method. Prior to the second step, the conductive paste is evaluated, and the nickel powder is coated with ceramic powder adhered to the particle surface, and the conductive paste having a coverage of 50% or more is selected and used. Manufacturing method of multilayer ceramic capacitor.

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