JP2005197019A - Conductive paste and laminated ceramic electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive paste hardly generating fault of internal structure and short circuit on a laminated ceramic capacitor, coping with the reduction of the size of the laminated ceramic capacitor and the increase of the capacity thereof, and suitable for the formation of an internal conductive layer. <P>SOLUTION: The laminated ceramic electronic component is manufactured by using the conductive paste containing conductive metal powder with average size of 0.2 μm or less synthesized by a liquid phase method, and conductive metal powder with average size of 0.2 μm or less synthesized by a gas phase method with a volume ratio ranging 1:9 to 9:1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a conductive paste and a multilayer ceramic electronic component such as a multilayer ceramic capacitor formed using the conductive paste, and in particular, the multilayer ceramic electronic component can be advantageously thinned and multilayered. It is for doing so.

  A conventional method for manufacturing a multilayer ceramic electronic component will be described by taking a multilayer ceramic capacitor as an example.

  First, a ceramic green sheet made of a dielectric ceramic raw material powder, an organic binder, and an organic solvent is prepared.

  On the other hand, a conductive paste made of a conductive metal powder, an organic binder, and an organic solvent is prepared.

  Next, a ceramic green sheet in which an internal conductor layer having a desired pattern is formed on the ceramic green sheet surface by a method such as screen printing using a conductive paste is obtained.

  Next, a predetermined number of the ceramic green sheets on which the internal conductor layers are formed are laminated and heat-pressed to form a laminated green block, which is then cut and separated into a predetermined shape to obtain a laminated green chip.

  Thereafter, the multilayer green chip is sintered at a predetermined firing temperature, and a conductive material is applied to both exposed end surfaces of the internal conductor layer to form external electrodes.

  In this way, a multilayer ceramic capacitor is obtained.

  In recent years, electronic devices are rapidly spreading, and these electronic devices are remarkably technologically innovative, and are required to be light, thin, small, and multifunctional. Under such circumstances, there is an increasing demand for miniaturization and large capacity in the multilayer ceramic capacitors that are used in large numbers.

  Therefore, in the multilayer ceramic capacitor, the ceramic layer is becoming thinner and multilayered for the purpose of reducing the size and increasing the capacity. For example, in a multilayer ceramic, a ceramic layer having a thickness of about 1.5 μm is about to be put into practical use.

  In order to reduce the thickness and thickness of ceramic layers, it is also important to reduce the thickness of the internal conductor layer. To this end, ceramic layers with different sintering behavior and the internal conductor layer have different shrinkage behaviors. Is as important as possible.

In order to solve these problems, as a method of adding ceramic powder to the conductive paste used to form the inner conductor layer, thereby bringing the shrinkage behavior of the inner conductor layer closer to the shrinkage behavior of the ceramic layer, For example, Patent Document 1 is known.
JP-A-6-290985

  However, in the multilayer ceramic capacitor, as the ceramic layer and the internal conductor layer are made thinner for the purpose of reducing the size and increasing the capacity, the above method cannot obtain a sufficient effect.

  By the way, as the conductive metal powder contained in the conductive paste used for forming the internal conductor layer used in the multilayer ceramic capacitor, the average particle size synthesized by the liquid phase method or the gas phase method exceeds 0.4 μm. A lot of nickel powder is used.

  Here, examples of the nickel powder synthesized by the liquid phase method include nickel powder synthesized by a spray method, an alkoxide method, or the like. Examples of the nickel powder synthesized by the vapor phase method include nickel powder synthesized by the CVD method.

  However, nickel powder synthesized by the liquid phase method has low crystallinity. Therefore, if the internal conductor layer is formed using a conductive paste containing nickel powder synthesized by the liquid phase method, the sintering shrinkage start temperature of the internal conductor layer is lowered because the nickel powder is easily sintered. As a result, the difference in sintering shrinkage start temperature with the ceramic layer becomes large, and internal structural defects such as cracks and delamination tend to occur.

  In addition, nickel powder synthesized by a vapor phase method has high reaction activity on the surface of the powder, and the powder tends to stick together. That is, it is easy to aggregate. For this reason, the average particle size of the powder synthesized by the vapor phase method is, for example, thin enough that the thickness of the internal conductor layer is 1.5 μm or less using a conductive paste containing nickel powder of 0.4 μm or more. If the coating thickness of the conductive paste is reduced in order to perform layering, the smoothness of the surface of the conductive paste film after drying, which should become the internal conductor layer, decreases, and the aggregate of the conductive paste film The convex portion of the internal conductor layer due to the piercing through the green sheet tends to increase short-circuit defects and lower the yield.

  Against this backdrop, when the ceramic layer is made thinner for the purpose of reducing the size and increasing the capacity of the multilayer ceramic capacitor, internal structural defects such as cracks and delamination, and short-circuit defects due to penetration do not occur. Realization of a conductive paste for forming an internal conductor layer is desired.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention includes a conductive metal powder that is not easily aggregated synthesized by a liquid phase method, a conductive metal powder that is synthesized by a vapor phase method and has high crystallinity, and an organic vehicle. A conductive paste in which the ratio of the conductive metal powder synthesized by the phase method and the conductive metal powder synthesized by the vapor phase method is in the range of 1: 9 to 9: 1 by volume, and the ceramic layer and the interior during firing The difference in sintering shrinkage start temperature with the conductor layer is reduced, and internal structural defects such as cracks and delamination are unlikely to occur, and the convex portion of the inner conductor layer penetrates the green sheet due to the aggregate of the conductive paste film. Therefore, it is possible to provide a multilayer ceramic electronic component that can reduce short-circuit defects due to the occurrence of the failure.

  According to the second aspect of the present invention, the use of nickel powder having an average particle size of 0.2 μm or less makes it difficult to form convex portions of the internal conductor layer even if aggregates are generated. Further, it is possible to further reduce short-circuit defects that penetrate the green sheet.

  According to a third aspect of the present invention, the conductive paste can be filtered with a filter having an opening of 5 μm or less to remove the agglomerated particles of the nickel powder, and the smoothness of the printed internal conductor layer. The short-circuit defect which penetrates and can penetrate can be further reduced.

  According to a fourth aspect of the present invention, there is provided a multilayer ceramic electronic component obtained by laminating, cutting and firing a ceramic green sheet having an internal conductor layer formed using the conductive paste according to the first aspect. In addition, it is possible to provide a multilayer ceramic electronic component that is less prone to internal structural defects such as cracks and delamination and has few short-circuit defects.

  The conductive paste of the present invention includes a conductive metal powder which is not easily aggregated synthesized by a liquid phase method and a conductive metal powder which is synthesized by a vapor phase method and has high crystallinity, and a ceramic layer and an internal conductor during firing. Because the difference in sintering shrinkage start temperature with the layer can be reduced, internal defects such as cracks and delamination are unlikely to occur, and short-circuit defects in which the convex portion of the internal conductor layer penetrates the green sheet are reduced. It has the effect of being able to.

(Embodiment 1)
Hereinafter, the first to fourth embodiments of the present invention will be described with reference to a multilayer ceramic capacitor as an example.

  First, ceramic slurry containing barium titanate having an average particle size of 0.5 μm, an additive, an organic binder, and an organic solvent were mixed to obtain a ceramic slurry. Using this ceramic slurry, a ceramic green sheet having a thickness set to 2.0 μm after firing was prepared by a doctor blade method.

  Further, as the conductive paste for forming the internal conductor layer, the powder having the average particle size shown in Table 1 and synthesized by the CVD method as the nickel powder by the vapor phase method and the alkoxide method as the nickel powder by the liquid phase method The conductive powder was prepared by mixing the powder synthesized in (1) at a volume ratio shown in (Table 1), adding a predetermined amount of an organic binder and an organic solvent, and kneading and dispersing.

  In Table 1, the sample described as “None” in the column of the synthesis method / average particle size means that the nickel powder of the synthesis method was not used.

  Using this conductive paste, the thickness was set so that the thickness after firing was 1.5 μm, and the internal conductor layer was formed on the ceramic green sheet in a predetermined pattern by screen printing.

  Next, 300 green sheets on which this internal conductor layer was formed were laminated, and a suitable number of plain ceramic green sheets were laminated as protective layers on the top and bottom to obtain a laminate. The obtained laminate was thermocompression bonded to obtain a laminate green block, and then cut and separated into a predetermined shape to obtain a laminate green chip. Thereafter, the multilayer green chip was fired at a maximum temperature of 1250 ° C. in a reducing atmosphere to obtain a sintered body. External electrodes were formed on both end faces from which the internal conductor layer of the obtained sintered body was exposed to obtain a multilayer ceramic capacitor.

  The outer dimensions of the multilayer ceramic capacitor thus obtained were 1.6 mm in width, 3.2 mm in length, and 1.5 mm in thickness.

  With respect to each sample of the multilayer ceramic capacitor thus obtained, the number of structural defects and the number of short-circuit defects were evaluated.

  More specifically, 100 samples are randomly extracted from the prepared samples and the number of samples in which structural defects such as cracks or delamination are generated is counted by observing the cross section under a microscope. The number of occurrences.

  Moreover, electrical characteristics were measured under the conditions of a temperature of 25 ° C., 1 kHz, and 1 Vrms, and the number of samples in which a short circuit failure occurred was counted, and the number of short circuit failures was obtained.

  From Table 1, Sample Nos. 1, 6, and 11 in which the internal conductor layer was formed using the conductive paste made only of nickel powder synthesized by the liquid phase method had a small number of short-circuit defects but the number of structural defects generated. I understand that there are many. This is because the nickel powder synthesized by the liquid phase method is easy to sinter, so the sintering shrinkage start temperature of the internal conductor layer is lowered, resulting in a large difference in the sintering shrinkage start temperature with the ceramic layer. This is because internal structural defects such as cracks and delamination are likely to occur.

  In the case of sample numbers 5, 10, and 13 using only nickel powder synthesized by the vapor phase method, the number of structural defects can be surely suppressed, but it can be seen that the number of short-circuit defects is large. This is because the nickel powder synthesized by the vapor phase method has a high reaction activity on the powder surface, and the powder tends to stick together (easy to aggregate), so the surface of the conductive paste film after drying that should become the internal conductor layer This is because the smoothness of the inner conductive layer is reduced and the convex portion of the inner conductive layer due to the aggregate of the conductive paste film penetrates the green sheet, thereby increasing short-circuit defects.

  Meanwhile, an internal conductor layer was formed using a conductive paste containing a nickel powder synthesized by a liquid phase method according to the present invention and a nickel powder synthesized by a gas phase method in a volume ratio of 1: 9 to 9: 1. In the case of sample numbers 2-4, 7-9, and 12, the number of structural defects can be reliably suppressed and the number of short-circuit defects can be reduced.

  From Table 1, it can be seen that Sample Nos. 2 to 4 using the conductive paste having an average particle diameter of nickel powder exceeding 0.2 μm have a large number of short-circuit defects.

  On the other hand, it can be seen that the number of short-circuit defects is reduced when a conductive paste having an average particle diameter of nickel powder of 0.2 μm or less is used as in sample numbers 7 to 9 and 12.

(Embodiment 2)
Next, by using a 0.2 μm nickel powder synthesized by a liquid phase method and a 0.2 μm nickel powder synthesized by a gas phase method at a volume ratio of 1: 1, the same method as in the first embodiment, After producing the conductive paste, the mixture was filtered using two types of filters having openings of 5 μm and 10 μm to produce two types of conductive paste.

  Using this conductive paste, an internal conductor layer was formed on a ceramic green sheet and laminated to obtain a multilayer ceramic capacitor.

  The number of structural defects and the number of short-circuit defects in each sample of the multilayer ceramic capacitor thus obtained were evaluated by the same method as in the first embodiment.

  The results are shown in (Table 2).

  It should be noted that in (Table 2), the sample described as “None” in the column of filtration means that the conductive paste was not filtered.

  From (Table 2), when the conductive paste was not filtered as in sample number 14, the number of short-circuit defects was 7/100, which was much less than the numbers in (Table 1). Not.

  In Sample No. 15 in which the internal conductor layer was formed using a conductive paste obtained by filtering a filter having an opening of 10 μm, the number of short-circuit defects was 6/100, which was not significantly reduced.

  On the other hand, in the case of Sample No. 16 using the conductive paste that was filtered using a filter having an opening of 5 μm, the number of short-circuit defects was 0, and an extremely good result was obtained.

  As described above, the multilayer ceramic capacitor has been described based on the embodiment. However, the same effect can be obtained not only for the multilayer ceramic capacitor described above but also for other multilayer ceramic electronic components such as a multilayer varistor and a multilayer chip thermistor.

  Further, in the above embodiment, nickel powder synthesized by CVD method as vapor phase synthetic metal powder and nickel powder synthesized by alkoxide method as liquid phase synthetic metal powder were used. The same effect can be obtained when using a metal powder produced by a liquid phase synthesis method.

  The conductive paste according to the present invention includes a conductive metal powder which is not easily aggregated synthesized by a liquid phase method and a conductive metal powder which is synthesized by a gas phase method and has a high crystallinity in a specific volume ratio. The difference in sintering shrinkage start temperature between the ceramic layer and the internal conductor layer at the time can be reduced, internal structural defects such as cracks and delamination are less likely to occur, and short-circuit defects can be reduced. In the multilayer ceramic electronic component, it is useful for reducing the size and increasing the capacity by thinning the ceramic layer and the internal conductor layer.

Claims (4)

At least a conductive metal powder synthesized by the liquid phase method, a conductive metal powder synthesized by the vapor phase method, and an organic vehicle, and the conductive metal powder synthesized by the liquid phase method and the conductive phase synthesized by the vapor phase method. The conductive paste in which the ratio of the conductive metal powder is in the range of 1: 9 to 9: 1 by volume. The conductive paste according to claim 1, wherein the conductive metal powder is nickel powder having an average particle size of 0.2 μm or less. The conductive paste according to claim 1, wherein the conductive paste is filtered with a filter having an opening of 5 μm or less. At least a conductive metal powder synthesized by the liquid phase method, a conductive metal powder synthesized by the gas phase method, and an organic vehicle, and the conductive metal powder synthesized by the liquid phase method and the conductivity synthesized by the gas phase method. A ceramic green sheet in which an internal conductor layer having a desired pattern is formed is laminated on a ceramic green sheet using a conductive paste having a volume ratio of 1: 9 to 9: 1 by volume, and then cut. Multilayer ceramic electronic parts obtained by firing.