JP2019200896A - Conductive paste - Google Patents

Abstract

To provide a conductive paste for forming an external electrode in a chip type ceramic electronic component and discourage generation of blister failure during burning.SOLUTION: There is provided a conductive paste used for forming an external electrode 2 in a chip type ceramic electronic component 1, containing a copper powder and a glass powder, in which the copper powder has particle diameter of 300 nm or less, particle diameter/crystalline diameter of over 1.0 and 3.8 or less, and volume percentage of the glass powder in total volume of the copper powder and the glass powder of 35 vol.% or less. When a burning process is conducted, nickel contained in an internal electrode 9 and copper contained in the conducive paste are scattered respectively in vicinity of an exposed end of the internal electrode 9 containing nickel in a component body 4, and a Ni-Cu alloy layer 11 is formed in the external electrode 2. A glass layer 12 derived from the glass powder contained in the conductive paste is formed in a region in contact with the external electrode 2 and the component body 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a conductive paste, and more particularly to a conductive paste used for forming an external electrode in a chip-type ceramic electronic component.

  For example, Japanese Unexamined Patent Application Publication No. 2011-26631 (Patent Document 1) describes a conductive paste containing copper powder, which is applied to form external electrodes in chip-type ceramic electronic components such as multilayer ceramic capacitors. Yes. In particular, in Patent Document 1, it is an object to provide oxidation resistance to copper powder, and in order to solve this problem, it is proposed to contain a specific amount of Bi and Mg inside the particles of copper powder. .

JP 2011-26631 A

  In order to reduce the external dimensions of the chip-type ceramic electronic component, it is considered as one effective means to reduce the thickness of the external electrode formed on the outer surface of the component body of the chip-type ceramic electronic component. In order to obtain an external electrode with high density, that is, with few defects and few voids while baking a conductive paste, it is necessary to atomize the copper powder and glass powder contained in the conductive paste. . For example, a method such as a liquid phase reduction method or a gas phase method (thermal plasma method) is known as a method for obtaining an atomized copper powder having a particle size of 1 μm or less.

On the other hand, if a fine copper powder having a particle diameter of 1 μm or less is used as the copper powder to be included in the conductive paste, gas is likely to be generated when the copper powder is sintered. There is. Examples of the gas that causes blisters include SO ₂ gas derived from sulfur contained as an impurity in copper powder, and CO ₂ gas derived from carbon contained in glass powder.

In order to suppress blister defects, it is considered effective to delay the start of sintering of fine copper powder. For example, by adding an oxide such as ZrO ₂ or Al ₂ O ₃ as a sintering retarder to the copper powder, if the start of sintering can be delayed, it is possible to secure a route for releasing the gas generated in the degreasing process. As a result, blister defects can be suppressed.

  However, according to the above-mentioned blister suppression technology, the contact performance of the external electrode with respect to the internal electrode that is to be electrically connected to the external electrode within the component body of the chip-type ceramic electronic component is deteriorated. You may encounter a problem at That is, there is a trade-off relationship between blister suppression and ensuring contact performance between the external electrode and the internal electrode.

  An object of the present invention is to provide a conductive paste for forming an external electrode that can make it difficult to cause blister defects during firing without relying on a sintering retarder.

  The present invention is directed to a conductive paste for forming external electrodes in a chip-type ceramic electronic component. The conductive paste contains copper powder and glass powder, and in order to solve the technical problems described above, the copper powder has a particle diameter of 300 nm or less, a particle diameter / crystallite diameter exceeding 1.0, and 3. 8 or less, and the volume ratio of the glass powder to the total volume of the copper powder and the glass powder is 35% by volume or less.

  According to the present invention, the conductive paste contains copper powder having a high crystallinity as a conductive component such that the particle diameter / crystallite diameter is 3.8 or less, although the particle diameter is as fine as 300 nm or less. Therefore, the progress of sintering can be moderated. Therefore, a sufficient path for escaping gas generated in the degreasing process in the baking process of the conductive paste can be secured, so that blister defects can be suppressed.

  Moreover, since the copper powder is fine particles having a particle diameter of 300 nm or less, gaps formed between the copper powder particles can be reduced. As a result, the amount of glass present in the gaps between the copper powder particles can be reduced to 35% by volume or less with the glass powder. Therefore, this can also be reduced for the gas derived from the glass powder that can be generated during firing. This also contributes to suppression of blister failures.

  Further, since the copper powder in the conductive paste is atomized to a particle size of 300 nm or less, the contact performance of the external electrode with respect to the internal electrode to be electrically connected to the external electrode can be improved, and the external In the electrode, high density such as high sealing property against moisture or the like can be realized.

It is sectional drawing which shows typically a part of chip-type ceramic electronic component 1 in which the external electrode 2 was formed using the electrically conductive paste by one Embodiment of this invention. It is a figure which shows the microscope picture which image | photographed the actual sample corresponded to the chip-type ceramic electronic component 1 shown in FIG. It is a figure for demonstrating the method to evaluate the adhering performance of the external electrode.

  The conductive paste according to one embodiment of the present invention is used to form external electrodes in chip-type ceramic electronic components. The conductive paste contains copper powder and glass powder, and further contains appropriate amounts of resin and solvent in order to provide paste properties.

  The copper powder contained in the conductive paste is a fine powder having a particle size of 300 nm or less. The particle diameter is obtained by photographing the surface of the copper powder with a scanning electron microscope (SEM) and using image analysis software. The crystallinity of the copper powder is high, and the particle size / crystallite size of the copper powder is 3.8 or less. Here, the crystallite diameter is obtained by measurement by an X-ray diffraction (XRD) method. In addition, since the crystallite diameter never becomes larger than the particle diameter, the particle diameter / crystallite diameter is a numerical value exceeding 1.0.

  The above-mentioned particle diameter / crystallite diameter is more preferably 1.1 or more and 2.0 or less. Thereby, the inhibitory effect of a blister malfunction can be heightened more. Moreover, it is preferable that the crystallite diameter of copper powder is 50 nm or more. This also contributes to further enhancing the effect of suppressing blister defects.

  The copper powder is preferably composed of spherical powder particles. According to this, since the glass ratio in the dry paint film of an electrically conductive paste can be reduced, glass content can be decreased, As a result, an external electrode can be densified. Therefore, for example, even in an ultra-small chip-type ceramic electronic component having a planar size of 0.2 mm × 0.1 mm, the external electrode fixing performance with respect to the ceramic surface of the component body in the chip-type ceramic electronic component is not reduced so much. Good electrical conductivity can be realized between the electrode and the internal electrode.

  Note that the conductivity between the external electrode and the internal electrode described above becomes better when the particle size of the copper powder is made smaller, for example, 100 nm, for example, 300 nm, and moreover, Thus, the fixing performance of the external electrode can be increased.

  The copper powder is preferably produced by a vapor phase method. According to the vapor phase method, as described above, a copper powder having a particle diameter of 300 nm or less and a particle diameter / crystallite diameter of 3.8 or less can be easily produced. In addition, according to the vapor phase method, it is possible to contain no or almost no impurities inside the powder particles of the copper powder. In particular, when chlorine is contained as an impurity, it can be made to contain only 0.01% by mass or less as the amount of chlorine ions. The amount of chlorine ions is a value measured by a combustion ion chromatography method. Moreover, when sulfur is contained as an impurity, it can be made to contain only 0.002 mass% or less as a sulfur amount. This amount of sulfur is a value measured by high frequency inductively coupled plasma optical emission spectrometry (ICP-AES).

  On the other hand, in the glass powder, the total volume of inorganic components in the conductive paste, that is, the volume ratio of the total volume of the copper powder and the glass powder is 35% by volume or less, preferably 10% by volume or more and 25% by volume or less. It is said. When the volume ratio of the glass powder is, for example, the upper limit of 35% by volume, there is no problem if the particle diameter of the copper powder is, for example, 100 nm or less, but when the particle diameter of the copper powder is, for example, 300 nm, However, the contact performance of the external electrode may deteriorate. Therefore, as described above, the volume ratio of the glass powder is preferably 10% by volume or more and 25% by volume or less.

  Preferably, the particle diameter of the glass powder is selected to be 1.0 μm or less. The particle diameter of the glass powder is also obtained by photographing the surface of the glass powder with an SEM and using image analysis software, as in the case of the copper powder.

  The glass powder is preferably made of B-Si glass. In this case, the B—Si based glass may contain Ba or Sr as an additive element.

  As described above, the conductive paste further includes appropriate amounts of a resin and a solvent. As the resin, known resins such as an acrylic resin, an ethyl cellulose resin, and a butyral resin are used. As the solvent, an alcohol solvent such as terpineol is preferably used. A dispersant may be added to the solvent.

  FIG. 1 is a cross-sectional view showing a part of a chip-type ceramic electronic component 1 on which external electrodes 2 are formed using the conductive paste described above. In FIG. 1, a chip-type ceramic electronic component 1 is schematically shown. Therefore, the form of each element shown in FIG. 1 and the dimensional ratio between each element may be different from the actual one (see FIG. 2).

  The chip-type ceramic electronic component 1 constitutes, for example, a multilayer ceramic capacitor, and includes a component body 4 in which a plurality of ceramic layers 3 are laminated. The component main body 4 includes a first main surface 5 and a second main surface 6 that face each other, a first end surface 7 that connects the first main surface 5 and the second main surface 6, and a second end that opposes the first end surface 7 (not shown). In addition, although not shown, the first and second side surfaces extend in parallel with the paper surface of FIG. 1 and face each other.

  Inside the component main body 4, a plurality of first internal electrodes 9 and second internal electrodes 10 are arranged along the stacking direction of the ceramic layers 3 while interposing a specific ceramic layer 3 between adjacent ones. Alternatingly arranged. The first internal electrode 9 is drawn out to the illustrated first end surface 7. On the other hand, the second internal electrode 10 is drawn out to a second end face (not shown). The internal electrodes 9 and 10 contain nickel as a conductive component.

  The illustrated external electrode, that is, the first external electrode 2 is formed on the first end surface 7 of the component main body 4 and is electrically connected to the first internal electrode 9. Although not shown, the second external electrode formed so as to face the first external electrode 2 is formed on the second end face of the component body 4 and is electrically connected to the second internal electrode 10. Yes. The first external electrode 2 and the second external electrode have substantially the same configuration. Therefore, in the following, the configuration of the first external electrode 2 will be described in detail, and the description of the configuration of the second external electrode will be omitted.

  The first external electrode 2 is formed so as to extend from the first end face 7 to the first and second main faces 5 and 6 adjacent thereto and a part of each of the first and second side faces. . In order to form the external electrode 2 having such a form, a conductive paste film is formed by applying the above-described conductive paste to a predetermined portion of the component body 4 by a dip method or the like, and this conductive paste film is fired. Is done. In the firing step, a temperature of 750 ° C. or lower is applied, for example, 700 ° C.

  When the above baking process is performed, in the conductive paste film, in the vicinity of the exposed end of the first internal electrode 9 on the first end surface 7, nickel contained in the internal electrode 9 and copper contained in the conductive paste Diffuse to each other, and the Ni—Cu alloy layer 11 is formed in the external electrode 2. The Ni—Cu alloy layer 11 is preferably free of voids and almost free of glass. The Ni—Cu alloy layer 11 functions to electrically connect the plurality of first internal electrodes 9 to each other, contributes to improvement in contact performance between the external electrode 2 and the internal electrode 9, and the external electrode 2 It also contributes to the improvement of moisture sealability.

  Further, in a region other than the region where the Ni-Cu alloy layer 11 is formed and in contact with the component body 4 in the external electrode 2, a glass layer 12 derived from the glass powder contained in the conductive paste is formed. The As shown in FIG. 1, the glass layer 12 is preferably a continuous layer, but may partially be interrupted. The glass layer 12 contributes to the improvement of the fixing performance of the external electrode 2 to the component body 4.

  FIG. 2 shows a photomicrograph of an actual sample corresponding to the chip-type ceramic electronic component 1 shown in FIG. In FIG. 2, a portion corresponding to the external electrode 2 and the component main body 4 shown in FIG. 1 is photographed. Although not particularly shown with a lead line, it can be seen in FIG. 2 that the first and second internal electrodes 9 and 10 are present in the component body 4. In the photomicrograph of FIG. 2, dark streaks or spots in the external electrode 2 are due to the presence of glass.

  A Ni—Cu alloy layer 11 is formed in the external electrode 2 near the exposed end of the first internal electrode 9 in the component main body 4. It can be seen that the Ni—Cu alloy layer 11 has no voids and almost no glass. Further, in a region other than the region where the Ni—Cu alloy layer 11 is formed and in contact with the component main body 4 in the external electrode 2, a glass layer 12 extending in a streak shape is formed.

  Further, it should be noted that no blister failure can be confirmed in the external electrode 2 of the chip-type ceramic electronic component 1 shown in FIG.

[Experimental example]
Next, experimental examples carried out using the conductive paste disclosed in this specification will be described.

  The copper powder contained in the conductive paste is manufactured by a vapor phase method and is made of spherical powder particles having a predetermined particle diameter and a predetermined crystallite diameter shown in the table below. Obtained from a vendor. Regarding the particle diameter of the copper powder, the surface of the copper powder was photographed with SEM, and an average value D50 of 500 particle diameters was determined using image analysis software, and this was used as the particle diameter. About crystallite diameter, crystallinity was measured using the Bruker X-ray-diffraction apparatus "D8 Advance", and the crystallite diameter was computed from this measured value with the dedicated software "TOPAS" made from Bruker.

  About the glass powder contained in an electrically conductive paste, the particle diameter is 1.0 micrometer or less, Comprising: The thing which consists of B-Si-Ba type | system | group glass was prepared.

  An appropriate amount of acrylic resin and terpineol were added to and mixed with the copper powder and glass powder described above to obtain a conductive paste.

  The conductive paste was evaluated for each item of “blister”, “contact performance”, and “adhesion performance” as shown in the table below.

  “Blister” is an evaluation of whether or not a blister failure has occurred. More specifically, a conductive paste was applied to both ends of a component main body having a plane dimension of 0.6 mm × 0.3 mm by a dip method and fired at a temperature of 720 ° C. to form external electrodes. Here, the thickness of the external electrode after firing on the end face of the component main body was set to 30 μm or 50 μm as described later. The appearance of 100 component bodies was observed, and even if one of them had a blister failure, it was determined to be defective and indicated by “x” in the table below.

  “Contact performance” is an evaluation of contact performance between an external electrode and an internal electrode. More specifically, a conductive paste is applied to both ends of a component body having a plane dimension of 0.2 mm × 0.1 mm by a dip method, and baked at a temperature of 720 ° C. to form an external electrode. A sample to be a multilayer ceramic capacitor having a capacitance of 10 nF was obtained. Next, a temperature of 150 ° C. was applied to the sample multilayer ceramic capacitor for 1 hour, and the initial capacity was measured after a further 24 hours. Next, the multilayer ceramic capacitor as a sample was charged with an applied voltage of 12.6 V that is twice the rated voltage for 5 seconds, and then left on a metal container to discharge electrons accumulated inside at 0 ohm. Thereafter, again, a temperature of 150 ° C. was applied to the multilayer ceramic capacitor as a sample for 1 hour, and the capacity was measured after 24 hours had elapsed. It was counted how many of 20 samples had this capacity decreased by 5% or more compared to the initial capacity described above. In the table below, when the number is 2 or more, “x” is displayed, when it is 1, “Δ” is displayed, and when it is 0, “◯” is displayed.

“Adhesion performance” is an evaluation of the adhesion performance of the external electrode to the component main body. More specifically, a conductive paste is applied to both ends of a component body having a plane dimension of 0.2 mm × 0.1 mm by a dip method, and baked at a temperature of 720 ° C. to form an external electrode. The external electrode was plated with Sn to produce a multilayer ceramic capacitor as a sample. Next, as shown in FIG. 3, the multilayer ceramic capacitor 22 is placed by placing the component body 23 of the multilayer ceramic capacitor 22 upright on the substrate 21 and applying solder 25 to the lower external electrode 24. Fixed to the substrate 21. In this state, as indicated by an arrow 26, the upper external electrode 27 was laterally pressed. The destruction mode caused by this lateral pushing
(1) Peeling at the interface between the substrate 21 and the solder 25,
(2) Peeling at the interface between the solder 25 and the plating film on the external electrode 24,
(3) peeling at the interface between the external electrode 24 and the component body 23, and (4) cracking of the component body 23,
It was classified into four. If there was even one sample that encountered the destruction mode (3) for 10 samples, it was determined to be defective, and “x” was displayed in the table below.

(Experimental example 1)
In Experimental Example 1, an external electrode was formed using a conductive paste containing copper powder having “particle diameter”, “crystallite diameter” and “particle diameter / crystallite diameter” as shown in Table 1. Moreover, the volume ratio of the glass powder to the total volume of the copper powder and the glass powder in the conductive paste was 25% by volume. In Experimental Example 1, the thickness of the fired external electrode on the end face of the component main body was set to 30 μm.

  In Table 1, Samples 1, 2 and 4 are within the scope of the present invention, and the copper powder has a “particle diameter” of 300 nm or less and a “particle diameter / crystallite diameter” exceeding 1.0 and Since the condition of 3.8 or less is satisfied, the “blister”, “contact performance” and “adhesion performance” are evaluated as “◯”.

  On the other hand, in the sample 3, since the “particle diameter / crystallite diameter” of the copper powder is 10.0 exceeding 3.8, the “blister” is evaluated as “x”.

  In Sample 5, since the “particle diameter / crystallite diameter” of the copper powder is 6.0 exceeding 3.8, “Blister” is evaluated as “x”. In Sample 5, since the “particle diameter” of the copper powder is larger than 100 nm in the case of Sample 2 such as 300 nm, the “adhesion performance” is further evaluated as “x”.

  In sample 6, since the “particle diameter” of the copper powder is 500 nm exceeding 300 nm and “particle diameter / crystallite diameter” is 5.0 exceeding 3.8, “blister”, “contact performance” The “adhesion performance” is evaluated as “x”.

  Sample 7 satisfies the condition that the “particle diameter / crystallite diameter” of the copper powder exceeds 1.0 and is 3.8 or less, but the “particle diameter” is 500 nm exceeding 300 nm. “Blister”, “Contact performance” and “Fixing performance” are evaluated as “x”.

(Experimental example 2)
In Experimental Example 2, an external electrode was formed using a conductive paste containing copper powder having “particle diameter”, “crystallite diameter” and “particle diameter / crystallite diameter” as shown in Table 2. Further, the volume ratio of the glass powder to the total volume of the copper powder and the glass powder in the conductive paste was set to 25% by volume as in the case of Experimental Example 1. In Experimental Example 2, the thickness of the external electrode after firing on the end face of the component main body was thicker than that in Experimental Example 1 and was 50 μm. It is estimated that the greater the thickness of the external electrode, the higher the risk of blister failure.

  In Table 2, all of the samples 11 to 18 have a “particle diameter” of 300 nm or less. Moreover, about the samples 11-13 and 15-18 except the sample 14 among the samples 11-18, it is said that copper powder has "particle diameter / crystallite diameter" exceeding 1.0 and 3.8 or less. The conditions are met and are within the scope of this invention.

  However, among the samples 11 to 13 and 15 to 18 within the scope of the present invention, the evaluation of “blister” is “x” for the samples 11 and 17. This is because the “particle diameter / crystallite diameter” of the copper powder is in the range of 1.1 or more and 2.0 or less in the samples 12, 13, 15, 16 and 18, whereas in the samples 11 and 17 , 1.1 and 2.0 or less, and 3.3 and 3.0, respectively.

  From this, the greater the thickness of the external electrode, the higher the risk of blister failure, so that the “particle diameter / crystallite diameter” of the copper powder is more than 1.0 and less than 3.8. It can be seen that it is desirable to narrow it to a range between 1.1 and 2.0.

  That is, in the samples 12, 13, 15, 16 and 18 in which the “particle diameter / crystallite diameter” of the copper powder is narrowed to a range of 1.1 or more and 2.0 or less, the thickness of the external electrode is increased to 50 μm. However, the evaluation of “Blista” is “○”.

(Experimental example 3)
In Experimental Example 3, an external electrode was formed using a conductive paste containing copper powder having “particle diameter”, “crystallite diameter” and “particle diameter / crystallite diameter” as shown in Table 3. In Experimental Example 3, as in Experimental Example 1, the thickness of the fired external electrode on the end surface of the component main body was set to 30 μm.

  In Experimental Example 3, the volume ratio of the glass powder to the total volume of the copper powder and the glass powder in the conductive paste was changed within the range of 5 to 35% by volume as shown in “Glass ratio” in Table 3.

  First, paying attention to the “particle diameter” of the copper powder, the samples 29 to 31 are out of the scope of the present invention in that they are 500 nm exceeding 300 nm. Therefore, the evaluation of at least one of “contact performance” and “adhesion performance” is “x”.

  On the other hand, Samples 21 to 28 are within the scope of the present invention. The copper powder has a “particle diameter” of 300 nm or less, a “particle diameter / crystallite diameter” exceeding 1.0 and 3.8 or less. The condition of being is satisfied. Although not shown in Table 3, in these samples 21 to 28, no blister failure occurred.

  However, among the samples 21 to 28, only the samples 22 to 24, 26, and 27 are evaluated as “◯” in the “contact performance” and “adhesion performance”. When attention is paid to the “glass ratio” in the samples 22 to 24, 26 and 27, the “glass ratio” is in the range of 10 to 25% by volume.

  On the other hand, in the samples 21 and 25 in which the “glass ratio” is less than 10% by volume and 5% by volume and 7% by volume, respectively, the “adhesion performance” is evaluated as “x”. The evaluation of “adhesion performance” was “x” because the “glass ratio” was relatively low, but the “glass ratio” was 7 vol%, which is higher than 5 vol% of the sample 21. It is estimated that the “adhesion performance” was evaluated as “x” because the “particle diameter” of the copper powder was 300 nm, which is larger than 100 nm of the sample 21.

  Moreover, in the sample 28 whose “glass ratio” is 35% by volume exceeding 25% by volume, the evaluation of “contact performance” is “Δ”. On the other hand, in the sample 24 whose “glass ratio” is also 35% by volume, the evaluation of “contact performance” is “◯”. This is not a problem if the “particle diameter” of the copper powder is relatively small as 100 nm as in the case of the sample 24 when the “glass ratio” is set to a relatively large 35 volume%. This indicates that there is a concern that the “contact performance” may be deteriorated when the “particle diameter” is relatively large at 300 nm. In other words, even when the “glass ratio” is relatively large, 35% by volume, it is shown that good contact performance can be obtained if the “particle diameter” of the copper powder is relatively small, such as 100 nm.

  As described above, as the chip-type ceramic electronic component to which the conductive paste according to the present invention is applied for forming the external electrode, the multilayer ceramic capacitor has been mainly exemplified and described. However, the conductive paste is not limited to other chip-type ceramic electronic components. It can also be used for forming external electrodes.

DESCRIPTION OF SYMBOLS 1 Chip-type ceramic electronic component 2 External electrode 4 Component main body 9,10 Internal electrode 11 Ni-Cu alloy layer 12 Glass layer

Claims (8)

A conductive paste for forming external electrodes in a chip-type ceramic electronic component,
Including copper powder and glass powder,
The copper powder has a particle size of 300 nm or less, a particle size / crystallite size of more than 1.0 and 3.8 or less,
The volume ratio of the glass powder in the total volume of the copper powder and the glass powder is 35% by volume or less.
Conductive paste.   The electrically conductive paste of Claim 1 whose said particle diameter / crystallite diameter of the said copper powder is 1.1 or more and 2.0 or less.   The conductive paste according to claim 1 or 2, wherein the crystallite diameter of the copper powder is 50 nm or more.   When the copper powder does not contain impurities or contains chlorine, the amount of chlorine ions is 0.01% by mass or less, and when sulfur is contained, the amount of sulfur is 0.002 mass. The electrically conductive paste in any one of Claim 1 thru | or 3 which contains only% or less.   The conductive paste according to claim 1, wherein the copper powder is formed of spherical powder particles.   The electrically conductive paste in any one of Claim 1 thru | or 5 whose volume ratio of the said glass powder to the total volume of the said copper powder and the said glass powder is 10 volume% or more and 25 volume% or less.   The electrically conductive paste in any one of Claim 1 thru | or 6 whose particle diameter of the said glass powder is 1.0 micrometer or less.   The conductive paste according to any one of claims 1 to 7, wherein the glass powder is made of B-Si glass.