JP2005071714A - Conductive paste and laminated ceramic electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste suitable for forming an internal conductor film thinly layered as a dielectric ceramic layer is thinly layered, in order to help the miniaturization of a laminated ceramic capacitor and enlarging its capacity. <P>SOLUTION: This conductive paste contains conductive powder such as nickel powder and an organic vehicle, and it also contains an organic barium compound and an organic hafnium compound. Each content of the barium compound and the organic hafnium compound in terms of an barium atom and a hafnium atom is 0.05-1.00 mol to 1.00 mol of the conductive powder, and the content of the organic hafnium compound in terms of the hafnium atom is 0.98-1.02 mol to 1.00 mol of the barium compound in terms of the barium atom. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a conductive paste and a multilayer ceramic electronic component configured by using the conductive paste for forming an internal conductor film. Particularly, the multilayer ceramic electronic component is advantageously thinned and multilayered. It is about the improvement to make it get.

  A multilayer ceramic electronic component body such as a multilayer ceramic capacitor has a multilayer structure including a plurality of laminated ceramic layers and an internal conductor film extending along an interface between the ceramic layers. Such a component body is generally formed by printing a film made of a conductive paste serving as an internal conductor film on a ceramic green sheet serving as a ceramic layer, and the ceramic green sheet formed with such a conductive paste film. Are produced by laminating a plurality of ceramic green sheets containing, and firing the resulting green laminate at a high temperature.

  As the conductive paste described above, a paste obtained by dispersing conductive powder in an organic vehicle composed of an organic binder and a solvent is used. In the conductive paste for the internal conductor film, a powder made of a noble metal such as palladium or platinum has been conventionally used as the conductive powder contained therein. However, in order to reduce the product cost, low-cost powder made of a base metal such as nickel has been used as the conductive powder contained in the conductive paste.

  On the other hand, there is a growing demand for miniaturization and multilayering of multilayer ceramic electronic components in the market, and in particular for multilayer ceramic capacitors, there is an increasing demand for miniaturization and large capacity. For this reason, the ceramic layer has been made thinner, and the internal conductor film has been made thinner as the ceramic layer is made thinner. In order to reduce the thickness of the internal conductor film, it is effective to atomize the conductive powder contained in the conductive paste.

  For example, when nickel powder is used as the conductive powder, the nickel itself is easily oxidized at a high temperature. Therefore, the firing process is performed in a non-oxidizing atmosphere such as an inert atmosphere or a reducing atmosphere. However, since the oxidation rate of nickel greatly depends on the specific surface area of the nickel powder, even if it is fired in a non-oxidizing atmosphere, the nickel is more easily oxidized as the nickel powder becomes more finely divided. Structural defects due to oxidation of the metal are more likely to occur.

  Also, in the firing process, as the nickel powder is atomized, the sintering and shrinkage of the nickel powder starts at a relatively early stage of the firing process. The difference in thermal shrinkage start temperature and shrinkage amount between the conductive paste film and the conductive paste film increases, resulting in a relatively large stress inside the laminate, which also causes structural defects such as delamination and cracks. It tends to occur.

In order to solve this problem, a ceramic raw material powder having the same or similar composition as the ceramic raw material powder contained in the ceramic layer is added to the conductive paste for the purpose of suppressing or controlling the sintering shrinkage of the conductive paste. (For example, see Patent Document 1). Thus, the ceramic raw material powder added to the conductive paste is present between the nickel particles in the conductive paste when the raw laminate is sintered, and acts as a pinning material, thereby forming the inner conductive film. The conductive paste film is considered to have a function of suppressing sintering shrinkage.
JP 2002-245874 A

  However, in a multilayer ceramic electronic component, in order to make the inner conductor film thinner, when a fine nickel powder having an average particle size of 0.2 μm or less is used in the conductive paste, the ratio of the nickel powder itself in accordance with the atomization. Since the surface area becomes larger and the contact frequency between nickel particles becomes higher in the conductive paste, it is difficult to exert a sufficient sintering suppression effect only by adding the ceramic raw material powder as described above. It becomes.

  Further, as the atomization of the nickel powder proceeds, spheroidization due to the sintering of the nickel powder is more likely to occur. This spheroidization of nickel hinders the continuity of the inner conductor film and reduces the coverage of the inner conductor film. Nickel spheroidization can be prevented to some extent by addition of the ceramic raw material powder as described above, but it becomes difficult to completely prevent the nickel powder from being further atomized. For this reason, as the thickness of the inner conductor film is reduced, the continuity of the inner conductor film is impaired and the coverage is lowered. As a result, in the multilayer ceramic capacitor, the designed capacitance may not be obtained.

  In addition, although the above-mentioned description was mainly performed about nickel powder, even if it is the case of powders, such as silver, a silver-palladium alloy, and copper, a substantially similar problem can be encountered.

  Accordingly, an object of the present invention is to provide a conductive paste capable of solving the above-described problems and a multilayer ceramic electronic component configured using the conductive paste.

  The conductive paste according to the present invention includes a conductive powder and an organic vehicle, and further includes an organic barium compound and an organic hafnium compound in order to solve the technical problems described above, and these organic barium compounds and barium of the organic hafnium compounds. Each content converted into atoms and hafnium atoms is 0.05 to 1.00 mol with respect to 1.00 mol of the conductive powder, and the content converted into hafnium atoms in the organic hafnium compound is organic. It is characterized by being 0.98 to 1.02 mol with respect to 1.00 mol in terms of barium atoms of the barium compound.

  As the conductive powder, nickel powder is preferably used.

  The conductive paste according to the present invention is particularly advantageously applied when the average particle size of the conductive powder contained therein is 0.2 μm or less.

  The conductive paste according to the present invention is advantageously used for forming an internal conductor film extending along a plurality of laminated ceramic layers.

  The present invention is also directed to a multilayer ceramic electronic component including a plurality of laminated ceramic layers and an inner conductor film extending along an interface between the ceramic layers. The multilayer ceramic electronic component according to the present invention is characterized in that the internal conductor film is obtained by firing the conductive paste according to the present invention.

  The above ceramic layer is preferably composed of a barium titanate ceramic.

  The multilayer ceramic electronic component according to the present invention is more advantageously applied to a multilayer ceramic capacitor. In this case, the inner conductor film is disposed so as to obtain a capacitance through the ceramic layer, and the multilayer ceramic electronic component is formed on the outer surface of the multilayer body including a plurality of ceramic layers, and is static. An external electrode is provided which is electrically connected to a specific one of the internal conductor films in order to extract the capacitance.

  Since the conductive paste according to the present invention has the above-described configuration, it does not adversely affect the electrical characteristics of the multilayer ceramic electronic component in which the conductive paste is used, for example, without changing the capacitance-temperature characteristics of the multilayer ceramic capacitor. Even if the conductive powder is atomized to have an average particle size of 0.2 μm or less, for example, the sintering can be suppressed.

  Therefore, it becomes possible to obtain high coverage simultaneously with the thinning of the inner conductor film formed using this conductive paste, and the structural defect of the multilayer ceramic electronic component configured using this conductive paste. Can be made difficult to occur.

  Therefore, when the conductive paste according to the present invention is used for forming an inner conductor film provided in a multilayer ceramic capacitor, it is advantageous to reduce the size and increase the capacity of the multilayer ceramic capacitor while maintaining high reliability. Can proceed.

  FIG. 1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 as an example of a multilayer ceramic electronic component constructed using the conductive paste according to the present invention.

  The multilayer ceramic capacitor 1 includes a multilayer body 2. The multilayer body 2 includes a plurality of laminated dielectric ceramic layers 3 and a plurality of internal conductor films 4 and 5 respectively formed along the interfaces between the plurality of dielectric ceramic layers 3.

  The inner conductor films 4 and 5 are formed so as to reach the outer surface of the multilayer body 2. More specifically, the inner conductor film 4 drawn to one end face 6 of the multilayer body 2 and the inner conductor film 5 drawn to the other end face 7 are disposed inside the multilayer body 2 via the dielectric ceramic layer 3. Thus, they are arranged alternately while facing each other so as to obtain a capacitance.

  In order to take out the above-mentioned capacitance, the external electrodes 8 and 7 are electrically connected to any one of the internal conductor films 4 and 5 on the end faces 6 and 7 on the outer surface of the multilayer body 2. 9 are formed. In addition, a plating layer made of nickel, copper, or the like is formed on the external electrodes 8 and 9 as necessary, and a plating layer made of solder, tin, or the like is further formed thereon. is there.

  Such a multilayer ceramic capacitor 1 is manufactured as follows, for example.

  For example, a slurry containing raw material powder for a dielectric ceramic such as barium titanate and appropriate additives is prepared, and the ceramic green sheet to be the dielectric ceramic layer 3 is formed by forming the slurry into a sheet. Is prepared. Next, conductive paste films for the internal conductor films 4 and 5 having a desired pattern are formed on the ceramic green sheet by printing or the like using a conductive paste.

  Next, as described above, the required number of ceramic green sheets each having a conductive paste film formed thereon are laminated, and ceramic green sheets having no conductive paste film formed thereon are laminated and thermocompression bonded. Thus, the integrated laminate 2 in a raw state can be obtained. In order to obtain this raw laminated body 2, it is often cut after the thermocompression bonding described above.

  Next, the raw laminate 2 is fired, thereby obtaining a sintered laminate 2. As will be described later, when the conductive paste for the inner conductor films 4 and 5 includes a base metal powder such as nickel powder as the conductive powder, this firing step is not performed in an inert atmosphere or a reducing atmosphere. It is carried out in an oxidizing atmosphere. In addition, when firing in a non-oxidizing atmosphere in this way, a reduction-resistant material is used as the ceramic raw material powder contained in the ceramic green sheet. In the laminated body 2 after sintering, the ceramic green sheet described above is sintered to become the dielectric ceramic layer 3, and the conductive paste film is sintered to become the internal conductor films 4 and 5.

  Next, external electrodes 8 and 9 are formed on end surfaces 6 and 7 of laminate 2 so as to be electrically connected to any one of internal conductor films 4 and 5, respectively. The external electrodes 8 and 9 are formed by applying and baking a conductive paste containing metal powder as a conductive component and added with glass frit.

  Next, nickel, copper or the like is plated on the external electrodes 8 and 9 to form first plating layers 10 and 11, and further, solder, tin or the like is plated on the second plating layer. 12 and 13 are formed. Thereby, the multilayer ceramic capacitor 1 shown in FIG. 1 is completed.

  In such a multilayer ceramic capacitor 1, the conductive paste used to form the inner conductor films 4 and 5 includes a conductive powder and an organic vehicle, an organic barium compound and an organic hafnium compound, and an organic paste. Each content in terms of barium atoms and hafnium atoms of the barium compound and organic hafnium compound is 0.05 to 1.00 mol with respect to 1.00 mol of the conductive powder, and the hafnium atom of the organic hafnium compound It is characterized in that the content in terms of is 0.98 to 1.02 mol with respect to 1.00 mol in terms of barium atoms of the organic barium compound.

  Examples of the organic barium compounds described above include barium alkoxides such as 1-methoxy-2-propoxide, ethoxide, and methoxide, barium salts such as abietic acid (rosin), octylic acid, naphthenic acid, stearic acid, and oleic acid. Fatty acid barium salts can be applied.

  Examples of the organic hafnium compound include 1-methoxy-2-propoxy hafnium, tetrabutoxy hafnium, tetraethoxy hafnium, tetrapropoxy hafnium, tetramethoxy hafnium, hafnium abietic acid, hafnium octylate, and hafnium naphthenate.

  The above-mentioned composition adopted in the conductive paste has been obtained based on knowledge obtained through the following experiment.

  First, hafnium was added as an organometallic compound solution to a conductive paste containing nickel powder, and a uniform mixture was prepared. The present inventor, when firing the conductive paste containing the hafnium component, hafnium oxide is generated in the process, and the hafnium oxide functions as a pinning point of ultrafine particles, thereby exhibiting a sintering suppressing effect. I thought.

  Therefore, when TMA (thermomechanical analysis) investigated the sintering shrinkage behavior of the green compact formed from the powder obtained by pulverizing the dry film of this conductive paste, the conductive paste added with the hafnium component was examined. According to the results, it was found that the sintering shrinkage start temperature shifts to the high temperature side compared to the additive-free one.

Next, a multilayer ceramic capacitor using a barium titanate (BaTiO ₃ ) -based dielectric material as the material of the dielectric ceramic layer and the conductive paste containing the above-described hafnium component as the material of the internal conductor film In the sintering process of the laminate, hafnium was diffused as hafnium oxide from the inner conductor film to the dielectric ceramic layer side and was dissolved in the titanium (B) site having a close ionic radius, so that the B site was excessive. As a result, there was a problem that the capacitance-temperature characteristics of the multilayer ceramic capacitor originally designed deviated.

  Therefore, when the barium component, which is the A site component, is added to the conductive paste as an organic compound together with the hafnium component, the conductive paste serving as the internal conductor film is not substantially changed without changing the capacitance-temperature characteristics of the multilayer ceramic capacitor. Sintering could be suppressed, and at the same time high coverage could be obtained in the inner conductor film.

  From this, it was found that it is preferable to add both a barium component and a hafnium component, that is, both an organic barium compound and an organic hafnium compound, to the conductive paste.

  Next, when the contents of these organic barium compounds and organic hafnium compounds were investigated, the following was found.

  First, if the molar ratio of barium / hafnium is greater than 1.02 or less than 0.98, the capacitance-temperature characteristics of the multilayer ceramic capacitor change significantly, depending on the amount of addition to the conductive paste. have done. From this, as described above, the content of the organic hafnium compound converted to hafnium atoms is in the range of 0.98 to 1.02 mol with respect to 1.00 mol converted to barium atoms of the organic barium compound. I knew I had to be chosen.

  In addition, when both the molar ratio of barium / nickel and the molar ratio of hafnium / nickel are less than 0.05, the effect of suppressing the sintering of nickel is not sufficient. The diffusion of barium and hafnium into the layer and the solid solution became excessive, so that the capacity-temperature characteristic was changed. For this reason, barium and hafnium are in a ratio close to stoichiometric, and must be 0.05 to 1.00 mol of content relative to 1.00 mol of nickel. all right.

Furthermore, as a result of electrolytic peeling of the fired laminate obtained by the above experiment and analyzing the vicinity of the interface between the inner conductor film and the dielectric ceramic layer by X-ray diffraction, BaHfO ₃ crystals were formed in a uniform state. It was confirmed that

Thus, by adding a barium component and a hafnium component as an organic compound solution to the conductive paste, compared to the case where a solid oxide such as a ceramic raw material powder common to the ceramic contained in the dielectric ceramic layer is added. The barium component and the hafnium component can be dispersed more uniformly in the conductive paste. The barium component and the hafnium component uniformly dispersed as droplets in the conductive paste produce ultrafine BaHfO ₃ crystals in the sintering process, and pinning between the nickel particles, thereby firing the nickel. It is possible to effectively suppress the ligation.

  As an additive to the conductive paste, in addition to the barium component and the hafnium component, the use of the solid oxide as described above is not prevented. By using such a solid oxide in combination, it is considered that sintering of the internal conductor film can be more effectively suppressed without impairing the electrical characteristics of the originally designed multilayer ceramic capacitor.

  In addition, although the above description was performed about the experiment which used nickel powder as electroconductive powder, the same result is obtained also about electroconductive powder which consists of other metals, such as silver, a silver-palladium alloy, and copper.

  Further, as described above, the multilayer ceramic capacitor has been mainly described. However, the conductive paste according to the present invention may be a multilayer ceramic electronic component including a plurality of laminated ceramic layers and an internal conductor film extending along an interface between the ceramic layers. For example, it can be advantageously used to form an internal conductor film in a multilayer ceramic electronic component other than a multilayer ceramic capacitor.

  Next, experimental examples carried out to determine the scope of the present invention will be described.

Experimental example

  First, a conductive paste for forming an inner conductor film of a multilayer ceramic capacitor was produced as follows.

  90% by weight of dihydroterpinyl acetate with 10% by weight of ethyl cellulose for 5.0% by weight of nickel powder having an average particle size of 0.15 μm and 5% by weight of barium titanate ceramic raw material powder having an average particle size of 0.03 μm The basic composition is obtained by adding 35% by weight of an organic vehicle dissolved in 15% by weight and 15% by weight of dihydroterpinyl acetate, and further adding 1-methoxy-2- Conductive paste well dispersed by adding propoxy barium and 1-methoxy-2-propoxy hafnium as an organic hafnium compound with an addition amount as shown in Table 1 and carrying out dispersion mixing treatment with a three-roll mill. Was made.

  In Table 1, “Ba molar ratio” indicates the content converted to barium atoms of 1-methoxy-2-propoxybarium with respect to 1.00 mol of nickel powder in terms of molar value, and “Hf molar ratio” The content of 1-methoxy-2-propoxy hafnium converted to hafnium atoms with respect to 1.00 mol of nickel powder is shown in terms of molar value. “Ba: Hf” is a molar ratio of the content of 1-methoxy-2-propoxybarium converted to barium atoms and the content of 1-methoxy-2-propoxyhafnium converted to hafnium atoms. It is a thing.

  On the other hand, a ceramic green sheet to be a dielectric ceramic layer of the multilayer ceramic capacitor was produced as follows.

  That is, a ceramic slurry is obtained by adding a polyvinyl butyral binder and an organic solvent such as ethanol to a reduction-resistant dielectric ceramic raw material powder mainly composed of barium titanate having an average particle diameter of 0.2 μm and wet-mixing it with a ball mill. It was. Next, this ceramic slurry was formed into a sheet shape with a thickness such that the thickness of the dielectric ceramic layer after firing was 1 μm by a doctor blade method, to obtain a rectangular ceramic green sheet.

  Next, the conductive paste described above was screen printed on the ceramic green sheet to form a conductive paste film. At this time, the thickness of the conductive paste film was set so that the nickel coating thickness measured using a fluorescent X-ray apparatus was 0.45 μm.

  Next, a plurality of ceramic green sheets including the ceramic green sheet on which the conductive paste film was formed were laminated, integrated by hot pressing, and then cut into a predetermined size to obtain a raw laminate. In this raw laminated body, the conductive paste film drawn to one end face and the conductive paste film drawn to the other end face were arranged alternately in the stacking direction.

Next, the raw laminate was heated to a temperature of 350 ° C. in a nitrogen atmosphere to decompose the binder, and then the H ₂ —N ₂ —H ₂ O gas having an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa was used. In a reducing atmosphere, the laminate was fired and sintered in a profile maintained at a maximum firing temperature of 1180 ° C. for 2 hours.

Next, a conductive paste containing a B ₂ O ₃ —Li ₂ O—SiO ₂ —BaO-based glass frit and containing silver as a conductive component is applied to both end faces of the sintered laminate. Baking was performed at a temperature of 600 ° C. in an atmosphere to form an external electrode electrically connected to the internal conductor film.

The outer dimensions of the multilayer ceramic capacitor thus obtained were 0.8 mm in width, 1.6 mm in length and 0.8 mm in thickness, and the thickness of the dielectric ceramic layer interposed between the internal conductor films was 1 μm. It was. The number of effective dielectric ceramic layers was 350, and the effective opposing area of the inner conductor film per layer was 0.9 mm ² .

  Next, for the obtained multilayer ceramic capacitor according to each sample, as shown in Table 1, “coverage”, “capacitance”, and “capacitance temperature change rate” were evaluated.

  More specifically, “coverage” is the process of peeling the multilayer ceramic capacitor according to each sample along the inner conductor film, taking a micrograph of the inner conductor film having holes, and subjecting this to image analysis processing. The amount covered with the inner conductor film is quantified.

  “Capacitance” is measured under the conditions of a temperature of 25 ° C., 1 kHz, and 1 Vrms by randomly extracting 200 samples from the obtained multilayer ceramic capacitor.

  “Capacitance temperature change rate” is based on the “capacitance” obtained as described above, and the capacitance is measured while applying a DC voltage of 4.0 V at a temperature of 85 ° C. Is what we asked for.

  Referring to Table 1, when comparing Samples 1 to 5 and Sample 8 as a comparative example, each of barium and hafnium in a molar ratio of 0.05 to 1.00 with respect to nickel in the conductive paste. According to Samples 1 to 5 added in the range, it can be seen that the coverage and the capacitance increase as the addition amount increases as compared with Sample 8 to which neither of these barium and hafnium is added. In addition, about a capacity | capacitance temperature change rate, the substantial difference is not recognized between the samples 1-5 and the sample 8. FIG.

  Next, comparing sample 3 with samples 6 and 7, in sample 3, barium and hafnium are equimolar (1: 1) to each other, such as 0.50 and 0.50, respectively, in molar ratios to nickel. Is added to the conductive paste so that the molar ratio of hafnium to barium is shifted to 0.98 and 1.02, respectively. However, even if Ba: Hf is shifted in the range of 1: 0.98 to 1: 1.02 as in samples 6 and 7, it is shown in Table 1 with sample 3 in the case of equimolarity. There is no significant difference in any of the evaluation items.

  On the other hand, in the sample 9 as a comparative example, each content of barium and hafnium with respect to nickel is added to the conductive paste so that the molar ratio is 0.03. Nevertheless, each evaluation result by this sample 9 is not substantially different from that of the non-added sample 8. Therefore, the addition amount of barium and hafnium added in the sample 9 is too small, and a sufficient effect is obtained. It turns out that it is not demonstrated.

  In the sample 10 as the next comparative example, each content of barium and hafnium with respect to nickel is added to the conductive paste so that the molar ratio is 1.20. According to this sample 10, the capacity temperature change rate is large. This is considered to be due to the excessive addition of barium and hafnium to nickel and the diffusion of these components into the dielectric ceramic layer.

  Next, in sample 11, the ratio of hafnium to barium is 0.90 in terms of molar ratio. In this sample 11, the coverage is lowered and the capacitance is relatively small. This is because barium is excessive with respect to hafnium, and the barium component diffused in the dielectric ceramic layer makes the ceramic composition ratio in the vicinity of the interface with the internal conductor film excessive at the A site. This is probably because the sintering was suppressed.

  Next, in sample 12, the ratio of hafnium to barium is 1.10 in molar ratio. According to this sample 12, hafnium is excessive with respect to barium, the ceramic composition of the dielectric ceramic layer in the vicinity of the interface with the internal conductor film is excessive at the B site, and sintering in the dielectric ceramic layer is promoted. This improves the capacitance, but the rate of change in capacitance temperature is higher than that of the additive-free sample 8.

1 is a cross-sectional view schematically illustrating a multilayer ceramic capacitor 1 as an example of a multilayer ceramic electronic component configured using a conductive paste according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Laminated body 3 Dielectric ceramic layer 4,5 Internal conductor film 8,9 External electrode

Claims (7)

  The conductive powder, the organic barium compound, the organic hafnium compound, and the organic vehicle, and the contents of the organic barium compound and the organic hafnium compound converted to barium atoms and hafnium atoms are both the conductive powder 1.00. It is 0.05-1.00 mol with respect to mol, and the content converted to hafnium atom of the organic hafnium compound is 0.00 with respect to 1.00 mol converted to barium atom of the organic barium compound. A conductive paste that is 98 to 1.02 moles.   The conductive paste according to claim 1, wherein the conductive powder is nickel powder.   The electrically conductive paste of Claim 1 or 2 whose average particle diameter of the said electrically conductive powder is 0.2 micrometer or less.   The conductive paste according to claim 1, 2, or 3, which is used for forming an internal conductor film extending along an interface between a plurality of laminated ceramic layers. A multilayer ceramic electronic component comprising a plurality of laminated ceramic layers and an inner conductor film extending along an interface between the ceramic layers,
The said internal conductor film is a multilayer ceramic electronic component obtained by baking the electrically conductive paste of Claim 1, 2 or 3.   The multilayer ceramic electronic component according to claim 5, wherein the ceramic layer is made of a barium titanate ceramic.   The inner conductor film is disposed so as to obtain a desired capacitance through the ceramic layer, and is further formed on an outer surface of a laminate composed of the plurality of ceramic layers, and the electrostatic 7. The multilayer ceramic electronic component according to claim 5, further comprising an external electrode electrically connected to a specific one of the internal conductor films for taking out a capacitance, thereby forming a multilayer ceramic capacitor.

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