JP2006024539A - Nickel paste for layered ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel paste that is capable of preventing the occurrence of structural defects such as delamination during a debinder process and a subsequent firing process for a layered ceramic capacitor, and that is suitable for formation of an inner electrode of nickel. <P>SOLUTION: The nickel paste is formed by dispersing a nickel powder in a vehicle in which a binder is dissolved in a solvent, and contains at least one sulfur-containing organic compound selected from among triazinethiol compounds and sulfate group-containing compounds, preferably in an amount of 0.01 to 1 weight % expressed in terms of sulfur with respect to nickel. This sulfur-containing organic compound suppresses the catalyst activity on the surface of nickel particles on the pyrolysis of the binder, and thereby prevents abrupt gas generation due to the partial pyrolysis of the binder in the course of the debinder process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nickel paste used to form internal electrodes of a multilayer ceramic capacitor (MLCC).

  In recent years, with the miniaturization of electronic devices, miniaturization of various electronic components has rapidly progressed, and miniaturization and high capacity have been promoted in multilayer ceramic capacitors. The multilayer ceramic capacitor has a structure in which ceramic dielectric layers and internal electrode layers are alternately stacked and sintered to be integrated. In addition, as a material for the internal electrode of the multilayer ceramic capacitor, a noble metal such as palladium has been conventionally used, but at present, nickel is mainly used for cost reduction.

  In general, in the manufacturing process of a multilayer ceramic capacitor, for example, a nickel paste in which nickel powder is dispersed in a vehicle as an internal electrode material is printed on a ceramic substrate or a ceramic green sheet, and this is thermocompression-bonded in a state of being stacked in multiple layers. And unite. Next, the binder is removed at 500 ° C. or lower in an oxidizing atmosphere or an inert atmosphere, and then heat firing is performed in a reducing atmosphere so that the internal electrodes are not oxidized.

  However, in the firing process, structural defects such as delamination and cracks are likely to occur due to a sintering-shrinkage mismatch between the ceramic dielectric layer and the nickel internal electrode layer. In particular, as the number of layers increases or the thickness of the ceramic dielectric layer decreases as the size and capacity increase, structural defects are more prominent.

  In order to solve this problem, it has been actively studied to reduce the thickness of the nickel internal electrode layer to alleviate the sintering-shrinkage mismatch. As one method for that purpose, there is a method (international publication No. 99/42237) in which the nickel powder has a spherical particle shape and a smooth surface to improve the filling property of the nickel particles.

  In addition, when nickel powder is oxidized in the debinding process, rapid sintering-shrinkage progresses simultaneously with reduction in the subsequent firing process in a reducing atmosphere, and as a result, the sintering-shrinkage mismatch increases and delamination occurs. Etc. are easily promoted. As a countermeasure against this, a method of adding phosphorus (P) to nickel powder (Japanese Patent Laid-Open No. 2002-150834) and a method of improving oxidation resistance by controlling an oxide film on the surface of nickel powder (Japanese Patent Laid-Open No. 2001-152202). Publication) etc. are proposed.

  However, in recent years, the ceramic dielectric layer and nickel internal electrode layer have been made thinner and the number of laminated ceramic dielectric layers and nickel internal electrode layers has been increasing. It has become difficult to eliminate the problem sufficiently.

International Publication No. 99/42237 Pamphlet JP 2002-150834 A JP 2001-152202 A

  The present invention has been made in view of the above-described conventional circumstances, and can prevent the occurrence of structural defects such as delamination in the debinding process of the multilayer ceramic capacitor and the subsequent firing process, and can form a nickel internal electrode. An object is to provide a suitable nickel paste.

  As a result of intensive studies on the generation of structural defects in the manufacturing process of the multilayer ceramic capacitor, the inventors have found that the sintering-shrinkage mismatch between the ceramic dielectric layer and the nickel internal electrode layer is due to the mutual relationship between the nickel powder and the binder in the debinding process. It was found that it changes depending on the action.

  That is, in the conventional nickel paste, the thermal decomposition of the binder is accelerated by the catalytic activity on the surface of the nickel particles in the middle of the debinding process. For example, when the binder is ethyl cellulose or the like, The outbreak was found to be triggered. The thermal decomposition of the binder at this point is limited to the vicinity of the surface of the nickel particles, and most of the other binders are not decomposed. Therefore, it has been found that the gas generated by partial decomposition of the binder is confined in place, and this gas pushes the space between the nickel internal electrode layer and the ceramic dielectric layer.

  Such rapid gas generation due to partial decomposition of the binder during the debinding process weakens the adhesion between the nickel internal electrode layer and the ceramic dielectric layer or causes partial delamination. This causes the structural defect of the multilayer ceramic capacitor through the firing step. In recent years, since the particle diameter of nickel particles is becoming smaller due to the further thinning of the nickel internal electrode layer, the catalytic activity on the surface of the nickel particles also increases, and the above phenomenon becomes an increasingly serious problem.

  In order to solve the above problems, the present inventors have conducted extensive research, and by adding a small amount of a sulfur-containing compound to the nickel paste, the catalytic activity on the surface of the nickel particles against the thermal decomposition of the binder is suppressed, and the debinding step It has been found that rapid gas generation due to partial thermal decomposition of the binder in the middle can be prevented, and the present invention has been completed.

  That is, the nickel paste for a multilayer ceramic capacitor provided by the present invention is characterized in that nickel powder is dispersed and a sulfur-containing organic compound is contained in a vehicle in which a binder is dissolved in a solvent. The content of the sulfur-containing organic compound is preferably 0.01 to 1% by weight in terms of sulfur with respect to nickel.

  In the nickel paste for multilayer ceramic capacitors according to the present invention, the sulfur-containing organic compound is preferably at least one selected from triazine thiols and sulfate group-containing compounds.

  According to the present invention, in the debinding process of the multilayer ceramic capacitor manufacturing, the thermal decomposition of the binder on the surface of the nickel particles in the paste and the accompanying rapid gas generation are suppressed, and structural defects such as delamination in the subsequent firing process Can be prevented. Therefore, without controlling the shape and particle size of the nickel powder, and adding a very small amount of sulfur-containing organic compound to the nickel paste, regardless of the binder or solvent used, a multilayer ceramic capacitor without structural defects can be easily obtained. Can be manufactured.

  The nickel paste for forming internal electrodes of the multilayer ceramic capacitor in the present invention is a paste in which nickel powder is dispersed in a vehicle in which a binder is dissolved in a solvent, and contains a sulfur-containing organic compound. The sulfur-containing organic compound added to the nickel paste is an organic compound containing sulfur (S), and it is necessary that it does not significantly affect the viscosity characteristics of the paste. In addition, the sulfur-containing organic compound cannot be expected to have a desired effect if it decomposes or disappears at a temperature below the temperature at which the binder component of the nickel paste starts to decompose in the binder removal process. May carbonize at high temperatures and partially inhibit the sintering of nickel powder. From such a viewpoint, the thermal decomposition temperature of the sulfur-containing organic compound is 200 ° C. or higher and 400 ° C. or lower in an atmosphere containing oxygen in the light of normal debinding conditions, and 200 ° C. in an inert atmosphere. As mentioned above, it is preferable that it is 700 degrees C or less.

For example, nickel sulfate and sulfur fine powders have a similar effect to prevent rapid gas generation, but from the viewpoint of being uniformly dispersed on the surface of finer nickel powder, they can be used as general paste solvents. Those that dissolve are preferred. Moreover, in order to make the addition amount as small as possible, it is preferable to selectively act on the surface of the nickel particles in a small amount and exhibit the effect of suppressing the thermal decomposition of the binder.

From such a viewpoint, as the sulfur-containing organic compound, triazine thiols and / or a sulfate group-containing compound can be preferably used, and one or more of these can be used. Triazine thiols are a group of compounds having a structure represented by the following chemical formula 1, wherein R represents a —SH group, a —NHR ₁ group, a —NR ₂ R ₃ group (where R ₁ , R ₂ , R ₃ means an aliphatic or aromatic hydrocarbon group).

Among the triazine thiols represented by Chemical Formula 1, 1,3,5-triazine-2,4,6-trithiol in which R is —SH is preferable as the triazine thiol from the viewpoint of the thermal decomposition temperature and solubility. 6-dibutylamino-1,3,5-triazine-2,4-dithiol in which R is —N (C ₄ H ₉ ) ₂ , 6-dihexylamino- in which R is —N (C ₆ H ₁₃ ) ₂ 1,3,5-triazine-2,4-dithiol, 6-dioctylamino-1,3,5-triazine-2,4-dithiol, where R is —N (C ₈ H ₁₇ ) ₂ , R is —N 6-didecylamino-1,3,5-triazine-2,4-dithiol which is (C ₁₀ H ₂₁ ) ₂ , 6-didodecylamino-1,3, wherein R is —N (C ₁₂ H ₂₅ ) ₂ Mention may be made of 5-triazine-2,4-dithiol.

  Besides these, 1,3,5-triazine-2,4,6-trithiol monosodium (FMN), 1,3,5-triazine-2,4,6-trithiol monopotassium, 3,5-triazine-2,4,6-trithiol monoethanolamine (FME), 1,3,5-triazine-2,4,6-trithiol diethanolamine (FDE), 1,3,5-triazine- 2,4,6-trithiol-triethylamine (F · TEA), 1,3,5-triazine-2,4,6-trithiol-octylamine, 1,3,5-triazine-2,4,6-trithiol Tetrabutylammonium salt, 1,3,5-triazine-2,4,6-trithiol bis (tetrabutylammonium salt) (F2A), 6-anilino-1,3,5-triazine-2,4-dithiol ( AF), -Anilino-1,3,5-triazine-2,4-dithiol monosodium (AMN), 6-anilino-1,3,5-triazine-2,4-dithiol triethylamine, 6-dibutylamino-1, 3,5-triazine-2,4-dithiol monosodium (DBMN), 6-dibutylamino-1,3,5-triazine-2,4-dithiol monoethanolamine (DBME), 6-dibutylamino-1 , 3,5-triazine-2,4-dithiol-ethylamine, 6-dibutylamino-1,3,5-triazine-2,4-dithiol-triethylamine, 6-dibutylamino-1,3,5-triazine-2 , 4-dithiol-butylamine (DBB), 6-dibutylamino-1,3,5-triazine-2,4-dithiol-tetrabutylammonium salt (DBA), 6-dibutylamino-1,3,5-triazine-2,4-dithiol-tetrabutylphosphonium salt, 6-diallylamino-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1, 3,5-triazine-2,4-dithiol monosodium (DAMN), 6-diallylamino-1,3,5-triazine-2,4-dithiol monoethanolamine (DAME), 6-diallylamino-1 , 3,5-triazine-2,4-dithiol-butylamine, 6-diallylamino-1,3,5-triazine-2,4-dithiol-ethylenediamine, 6-diallylamino-1,3,5-triazine-2 , 4-dithiol-ethylenetriamine, 6-octylamino-1,3,5-triazine-2,4-dithiol, 6-octylamino-1,3,5-triazine-2, - it can be used as the dithiol monosodium.

The sulfate group-containing compound includes an aliphatic or aromatic hydrocarbon compound containing sulfate group SO ₃ or a salt thereof. Specifically, sodium dodecyl sulfate CH ₃ (CH ₂ ) ₁₁ SO ₃ Na, dodecylbenzene Examples thereof include sodium sulfonate C ₁₂ H ₂₅ C ₆ H ₄ SO ₃ Na.

  Although it is not clear about the action of these sulfur-containing organic compounds to suppress rapid gas generation during the debinding process, the portion containing sulfur such as SH of triazine thiols and SO3 of sulfate group-containing compounds is nickel particles. It is thought that it is adsorbed on the surface and loses its catalytic activity to prevent partial thermal decomposition of the binder. In particular, triazine thiol exhibits strong reactivity with metals through S in the SH group, and is therefore considered to be more strongly adsorbed on the surface of the nickel powder particles. In addition, nickel particles adsorbed with sulfur-containing organic compounds also have the advantage that the dispersibility in the vehicle and the corrosion resistance are also improved.

  The content of the sulfur-containing organic compound in the nickel paste is preferably in the range of 0.01 to 1% by weight and more preferably in the range of 0.02 to 0.5% by weight in terms of sulfur with respect to the nickel weight. When the content of the sulfur-containing organic compound is less than 0.01% by weight, the effect of suppressing the thermal decomposition of the binder becomes insufficient. Further, even if the content exceeds 0.5% by weight, an increase in the effect is not recognized, and the cost is simply increased. Further, if the content exceeds 1% by weight, the possibility of adversely affecting the characteristics of the electronic component is increased. Absent. Depending on the other materials combined with the nickel paste and the process conditions using the paste, the sulfur-containing organic compound may be applied even when the content exceeds 1% by weight.

In this way, since the sulfur-containing organic compound acts by concentrating the sulfur-containing portion such as SH or SO _{3 on} the surface of the nickel particles, a sufficient effect can be obtained with an extremely small addition amount. It is possible to obtain a sufficient effect with a much smaller amount as compared with the case of evenly dispersing the material. Moreover, if the paste contains excessive components other than nickel, the reliability of the final electronic component may be adversely affected. This is also advantageous.

  As a method for adding the sulfur-containing organic compound, it is preferable to add it simultaneously with other additives at the time of preparing the paste. For example, a method of adding a predetermined amount to a paste prepared as usual and kneading again can be employed. However, from the viewpoint of effectively uniformly coating nickel particles with a sulfur-containing organic compound, the binder is a solvent. It is preferable to dissolve the sulfur-containing organic compound in advance in a vehicle dissolved in the solution. In addition, when dispersants are used as additives, they may be preferentially adsorbed on the nickel particles to inhibit the action of the sulfur-containing organic compound. It is desirable to adjust the order.

  In addition, about the solvent, binder, and nickel powder which comprise a nickel paste, the thing similar to the past can be used. For example, as the solvent, terpineol, butyl carbitol acetate, butyl carbitol, dihydroterpineol, dihydroterpineol acetate, and other paraffinic hydrocarbon solvents can be used. As the binder, celluloses such as ethyl cellulose, polyvinyl butyral, and the like can be used.

  As a standard indicating the degree of partial pyrolysis of the binder and the accompanying rapid gas generation during the nickel binder debinding process (around 260 ° C.), the temperature reached 300 ° C. from the thermal decomposition temperature of the binder and the start of debinding. The weight reduction amount of the binder at the time was measured, and the influence of the nickel particles in the slurry on the thermal decomposition and the effect of the sulfur-containing organic compound added to the paste were evaluated.

[Control example]
First, as a control example, a vehicle composed of ethyl cellulose and terpineol (excluding nickel powder) was applied to a PET film with a thickness of 100 μm using an applicator, dried at 90 ° C. for 6 hours, and then only a dried film. Was pulverized in a mortar and passed through a 100 mesh sieve to obtain a dry vehicle powder.

  In order to evaluate the thermal decomposition temperature of the binder and the amount of weight loss at 300 ° C. for this dried vehicle powder, a nitrogen flow rate of 200 ml / min was used using a differential thermal analyzer (TG-DTA2000SA, manufactured by Bruker AXS). In a nitrogen stream, the analysis was evaluated at a heating rate of 5 ° C./min.

  As a result, the decomposition temperature of the binder was 325 ° C., the weight reduction proceeded almost uniformly, and the partial thermal decomposition of the binder and the accompanying rapid gas generation did not occur. Further, the theoretical weight reduction amount of the binder in the nickel paste was determined from the weight reduction amount at 300 ° C. in the differential thermal analysis of the vehicle dry powder, and found to be 0.06% by weight.

[a formula]
Theoretical weight loss of binder in nickel paste (% by weight) = weight loss at 300 ° C. (% by weight) in differential thermal analysis of vehicle dry powder × weight ratio of binder in nickel paste

[Examples 1 to 10]
50 parts by weight of nickel powder (manufactured by Sumitomo Metal Mining Co., Ltd., product name YH-641, average particle size 0.4 μm), 50 parts by weight of a vehicle comprising the same ethyl cellulose and terpineol as in the control example (however, the weight of ethyl cellulose is Ni And a triazine thiol (TST) group shown in Table 1 below were added at the same time, and a three-roll mill (manufactured by Inoue Mfg. Co., Ltd., 43/4 × 11 S-type roll machine). ) And kneading with a FOG gauge (grain gauge) until the particle size is 10 μm or less to prepare a nickel paste.

The type of triazine thiol (TST) used is 6-dibutylamino-1, which is R = —N (C ₄ H ₉ ) ₂ according to R in the chemical formula 1, as shown in Table 1 below. 3,5-triazine-2,4-dithiol (DB), 6-dihexylamino-1,3,5-triazine-2,4-dithiol (DH) in which R = —N (C ₆ H ₁₃ ) ₂ , 6-Dioctylamino-1,3,5-triazine-2,4-dithiol (DO), where R = —N (C ₈ H ₁₇ ) ₂ , 6—R = —N (C ₁₀ H ₂₁ ) ₂ Didecylamino-1,3,5-triazine-2,4-dithiol (DD), 6-didodecylamino-1,3,5-triazine-2,4- in which R = —N (C ₁₂ H ₂₅ ) ₂ It was either dithiol (DL). Moreover, the addition amount of the triazine thiol (TST) shown in Table 1 is converted into sulfur by the amount with respect to the nickel weight.

  The obtained nickel pastes of Examples 1 to 10 were applied on a PET film with a thickness of 100 μm using an applicator and dried at 90 ° C. for 6 hours in the same manner as in the control example. Thereafter, only the dried film was pulverized in a mortar and passed through a 100 mesh sieve to obtain a dried nickel paste powder.

  About these nickel paste dry body powders, in order to evaluate the thermal decomposition temperature and weight reduction of a binder and to compare with the said comparative example, using a differential thermal analyzer (Bruker AXS, TG-DTA2000SA), nitrogen flow rate Analysis and evaluation were conducted at a heating rate of 5 ° C./min in a nitrogen stream of 200 ml / min.

  Further, from the weight loss amount at 300 ° C. determined by differential thermal analysis (% by weight) and the theoretical weight loss amount determined in the above control example, the theoretical weight loss amount (the weight loss amount at 300 ° C. The weight loss ratio at 300 ° C. (ie, 06 wt%) was 1 (that is, the weight loss (wt%) / theoretical weight loss (wt%) at 300 ° C.)). These evaluation results are summarized in Table 1 below.

[Example 11]
The same procedure as in Example 4 was performed except that the addition time of triazine thiols was after paste kneading. That is, 50 parts by weight of nickel powder (Sumitomo Metal Mining Co., Ltd., product name YH-641, average particle size 0.4 μm), 50 parts by weight of a vehicle composed of ethyl cellulose and terpineol (the weight of ethyl cellulose is 3% by weight with respect to Ni) %), And kneading in a three-roll mill, and then adding and kneading DB of triazine thiol (TST) to the obtained paste.

  About the obtained nickel paste, a nickel paste dry body powder was produced in the same manner as described above, and the thermal decomposition temperature of the binder, the weight loss at 300 ° C., and the weight loss ratio were determined by differential thermal analysis. It was shown together.

[Example 12]
A nickel paste was prepared in the same manner as in Example 4 except that sodium dodecyl sulfate (SDS) was used instead of triazine thiol (TST). About the obtained nickel paste, a nickel paste dry body powder was produced in the same manner as described above, and the thermal decomposition temperature of the binder, the weight loss at 300 ° C., and the weight loss ratio were determined by differential thermal analysis. It was shown together.

[Comparative example]
As a comparative example, a conventional nickel paste to which neither triazine thiol (TST) or sodium dodecyl sulfate (SDS) was added was prepared. That is, 50 parts by weight of nickel powder (Sumitomo Metal Mining Co., Ltd., product name YH-641, average particle size 0.4 μm) and 50 parts by weight of a vehicle composed of ethyl cellulose and terpineol (however, the weight of ethyl cellulose is less than that of Ni). Adjusted to 3% by weight) and kneaded in a three-roll mill to obtain a paste.

  The nickel paste of this comparative example was applied to a PET film with a thickness of 100 μm using an applicator and dried at 90 ° C. for 6 hours, and the dried film alone was pulverized in a mortar. And passed through a 100 mesh sieve to obtain a dried nickel paste powder.

  Also for the nickel paste dry body powder of this comparative example, the thermal decomposition temperature of the binder, the weight loss at 300 ° C., and the weight loss ratio were evaluated by differential thermal analysis, as in the above comparative example and example. The results are also shown in Table 1 below.

  As can be seen from the evaluation results of the comparative examples in Table 1, the conventional nickel paste to which neither triazine thiol (TST) or sodium dodecyl sulfate (SDS) is added is 325 ° C. which is a normal binder decomposition temperature. In addition, the binder was rapidly pyrolyzed at about 260 ° C. along the way. As a result, the weight loss amount at 300 ° C. is as large as 1.75% by weight, and the weight loss ratio at 300 ° C. when the theoretical weight loss amount in the vehicle-only control example is 1 is as large as 29.1. became. For this reason, it can be understood that structural defects such as delamination are likely to occur in the multilayer ceramic capacitor due to the generation of a large amount of gas.

  On the other hand, in the nickel paste of each example according to the present invention, by adding either triazine thiol (TST) or sodium dodecyl sulfate (SDS), compared with the nickel paste of the comparative example not containing these, Also, the weight loss ratio at 300 ° C. was greatly reduced. In addition, the thermal decomposition of the binder at about 260 ° C. does not occur, the weight reduction proceeds almost uniformly, and the decomposition temperature of the binder is higher than 325 ° C. It can be seen that the generation of gas is suppressed. Accordingly, it can be seen that in the multilayer ceramic capacitor finally obtained through the subsequent firing step, the occurrence of structural defects such as delamination is reduced and improved.

Claims (3)

  A nickel paste for use in forming an internal electrode of a multilayer ceramic capacitor, wherein nickel powder is dispersed in a vehicle in which a binder is dissolved in a solvent and a sulfur-containing organic compound is contained. .   2. The nickel paste for a multilayer ceramic capacitor according to claim 1, wherein the content of the sulfur-containing organic compound is 0.01 to 1% by weight in terms of sulfur with respect to nickel. The nickel paste for multilayer ceramic capacitors according to claim 1 or 2, wherein the sulfur-containing organic compound is at least one selected from triazine thiols and a sulfate group-containing compound.