JP6787364B2 - Conductive paste - Google Patents

Description

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

For example, Japanese Patent Application Laid-Open No. 2011-26631 (Patent Document 1) describes a conductive paste containing copper powder, which is applied to form an external electrode in a chip-type ceramic electronic component such as a multilayer ceramic capacitor. There is. In particular, Patent Document 1 has an object of imparting oxidation resistance to copper powder, and in order to solve this problem, it has been proposed to contain a specific amount of Bi and Mg inside the particles of the copper powder. ..

Japanese Unexamined Patent Publication No. 2011-26631

In order to reduce the external dimensions of the chip-type ceramic electronic component, it is considered as one of the 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. It is necessary to atomize the copper powder and glass powder contained in the conductive paste in order to obtain an external electrode having high density, that is, few defects and few voids, while thinning the film, by baking 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 a copper powder having a particle size of 1 μm or less.

On the other hand, when fine copper powder having a particle diameter of 1 μm or less is used as the copper powder to be contained in the conductive paste, gas is likely to be generated when the copper powder is sintered, which causes a defect due to a blister on the external electrode. There is. Examples of the gas that causes blister 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.

It is considered effective to delay the start of sintering of fine copper powder in order to suppress blister defects. For example, if the start of sintering can be delayed by adding an oxide such as ZrO ₂ or Al ₂ O _{3 to} the copper powder as a sintering delay agent, it is possible to secure a path for releasing the gas generated in the degreasing process. Therefore, it is possible to suppress blister defects.

However, according to the above-mentioned blister suppression technology, the contact performance of the external electrode with respect to the internal electrode that should be electrically connected to the external electrode inside the component body of the chip-type ceramic electronic component is deteriorated, and the quality aspect is improved. You may encounter challenges in. That is, there is a trade-off relationship between suppressing the blister and ensuring the 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, which can prevent blister defects during firing without relying on a sintering retarder.

The present invention is directed to conductive pastes for forming external electrodes in chip-type ceramic electronic components. The conductive paste contains copper powder and glass powder, and in order to solve the above-mentioned technical problems, the copper powder has a particle diameter of 300 nm or less, a particle diameter / crystallite diameter of 1.1 or more and 2.0. It is characterized in that 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 as a conductive component a copper powder having a particle size of 300 nm or less, which is fine, but has a particle size / crystallite diameter of 2.0 or less, which is highly crystalline. Therefore, the progress of sintering can be slowed down. Therefore, it is possible to sufficiently secure a path for releasing the gas generated in the degreasing process in the firing process of the conductive paste, so that the blister defect can be suppressed.

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

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 electrode can be contacted with the external electrode. In the electrode, it is possible to realize high density such as high sealing property against moisture and the like.

FIG. 5 is a cross-sectional view schematically showing a part of a chip-type ceramic electronic component 1 on which an external electrode 2 is formed by using a conductive paste according to an embodiment of the present invention. It is a figure which shows the micrograph which took the actual sample corresponding to the chip type ceramic electronic component 1 shown in FIG. It is a figure for demonstrating the method of evaluating the sticking performance of an external electrode 24.

The conductive paste according to one embodiment of the present invention is used to form an external electrode in a chip-type ceramic electronic component. The conductive paste contains copper powder and glass powder, and further contains an appropriate amount of resin and solvent in order to impart paste property.

The copper powder contained in the conductive paste is a fine powder having a particle size of 300 nm or less. The particle size was determined by photographing the surface of the copper powder with a scanning electron microscope (SEM) and using image analysis software. Further, the crystallinity of the copper powder is high, and the particle size / crystallite diameter of the copper powder is 2.0 or less. Here, the crystallite diameter is measured and obtained by the X-ray diffraction (XRD) method. Since the crystallite diameter does not become larger than the particle diameter, the particle diameter / crystallite diameter is a value exceeding 1.0.

In the present invention, the above-mentioned particle diameter / crystallite diameter is 1.1 or more , and 2.0 or less as described above . As a result, it is possible to prevent blister defects from occurring . Further, the crystallite diameter of the copper powder is preferably 50 nm or more. This also contributes to further enhancing the effect of suppressing blister defects.

The copper powder preferably consists of spherical powder particles. According to this, since the glass ratio in the dry coating film of the conductive paste can be reduced, the glass content can be reduced, and as a result, the external electrode can be densified. Therefore, even in an ultra-small chip-type ceramic electronic component having a plane dimension of 0.2 mm × 0.1 mm, for example, the external electrode does not significantly deteriorate the adhesion performance of the external electrode to the ceramic surface of the component body in the chip-type ceramic electronic component. Good conductivity can be achieved between the electrodes and the internal electrodes.

It should be noted that when the particle size of the copper powder is made smaller, for example, 100 nm than, for example, 300 nm, the conductivity between the external electrode and the internal electrode described above becomes better, and the above-mentioned It is possible to improve the fixing performance of the external electrode.

The copper powder is preferably produced by the 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 2.0 or less can be easily produced. Further, according to the vapor phase method, impurities can be contained or hardly contained in the powder particles of the copper powder. In particular, when chlorine is contained as an impurity, the amount of chlorine ions can be reduced to 0.01% by mass or less. The amount of chlorine ions is a value measured by a combustion ion chromatography method. When sulfur is contained as an impurity, the amount of sulfur can be limited to 0.002% by mass or less. The amount of sulfur is a value measured by high frequency inductively coupled plasma emission spectroscopy (ICP-AES).

On the other hand, in the glass powder, the total volume of the inorganic components in the conductive paste, that is, the volume ratio to 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 that. 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 size of the copper powder is, for example, 100 nm or less, but when the particle size of the copper powder is, for example, 300 nm, the internal electrode 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 size of the glass powder is selected to be 1.0 μm or less. The particle size of the glass powder was 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.

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

As mentioned above, the conductive paste further contains an appropriate amount of resin and solvent. As the resin, known resins such as acrylic resin, ethyl cellulose resin, and butyral resin are used. As the solvent, an alcohol solvent such as tarpineol 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 an external electrode 2 is formed by using the above-mentioned conductive paste. In FIG. 1, a chip-type ceramic electronic component 1 is schematically illustrated. Therefore, the form of each element shown in FIG. 1 and the dimensional ratio between each element may differ 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 body 4 has a first main surface 5 and a second main surface 6 facing each other, a first end surface 7 connecting between them, and a second surface (not shown) facing the first end surface 7. Further, although not shown, it has a first side surface and a second side surface which extend parallel to the paper surface of FIG. 1 and face each other.

Inside the component body 4, a plurality of first internal electrodes 9 and second internal electrodes 10 are provided along the stacking direction of the ceramic layers 3 while interposing a specific ceramic layer 3 between adjacent objects. They are arranged alternately. The first internal electrode 9 is drawn out to the first end face 7 shown in the figure. On the other hand, the second internal electrode 10 is pulled 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 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. There is. The first external electrode 2 and the second external electrode have substantially the same configuration. Therefore, the configuration of the first external electrode 2 will be described in detail below, and 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 surface 7 to the first and second main surfaces 5 and 6 adjacent thereto and each part of the first and second side surfaces. .. In order to form the external electrode 2 in such a form, a conductive paste film is formed by applying the above-mentioned conductive paste to a predetermined portion of the component main body 4 by a dip method or the like, and the conductive paste film is fired. Will be done. In the firing step, a temperature of 750 ° C. or lower is applied, for example 700 ° C.

When the above-mentioned firing step is carried out, in the vicinity of the exposed end of the first internal electrode 9 on the first end surface 7 of the conductive paste film, nickel contained in the internal electrode 9 and copper contained in the conductive paste are present. Are diffused to each other, and a Ni—Cu alloy layer 11 is formed in the external electrode 2. It is preferable that the Ni—Cu alloy layer 11 has no voids and almost no glass. The Ni—Cu alloy layer 11 functions to electrically connect the plurality of first internal electrodes 9 to each other, contributes to the improvement of the contact performance between the external electrode 2 and the internal electrode 9, and also contributes to the improvement of the contact performance between the external electrode 2 and the external electrode 2. Also contributes to the improvement of moisture sealing property.

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. Ru. As shown in FIG. 1, the glass layer 12 is preferably a continuous layer, but may be partially interrupted. The glass layer 12 contributes to improving 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 by a leader line, in FIG. 2, it is recognized that the first and second internal electrodes 9 and 10 are present in the component body 4. In the photomicrograph of FIG. 2, the 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 vicinity of the exposed end of the first internal electrode 9 in the component body 4 of the external electrode 2. It is recognized that the Ni—Cu alloy layer 11 has no voids and almost no glass is present. 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 pattern is formed.

Further, it should be noted that the external electrode 2 of the chip-type ceramic electronic component 1 shown in FIG. 2 cannot be confirmed to have a blister defect.

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

The copper powder contained in the conductive paste is produced by the vapor phase method and is composed 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 size of the copper powder, the surface of the copper powder was photographed by SEM, and an average value D50 of 500 points of the particle size was obtained using image analysis software, and this was used as the particle size. Regarding the crystallite diameter, the crystallinity was measured using Bruker's X-ray diffractometer "D8 Advance", and the crystallite diameter was calculated from this measured value by Bruker's dedicated software "TOPAS".

As the glass powder contained in the conductive paste, a glass powder having a particle size of 1.0 μm or less and made of B—Si—Ba based glass was prepared.

A conductive paste was obtained by adding an appropriate amount of acrylic resin and tarpineol to the above-mentioned copper powder and glass powder and mixing them.

In addition, the conductive paste was evaluated for each item of "blister", "contact performance" and "sticking performance" as shown in the table below.

"Blister" is an evaluation of the presence or absence of a blister defect. More specifically, a conductive paste was applied to both ends of a component 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 an external electrode. Here, the thickness of the external electrode after firing on the end face of the component body is set to 30 μm or 50 μm as described later. The appearance of 100 parts was observed, and if any blister defect occurred, it was judged to be defective, and it is indicated by "x" in the table below.

"Contact performance" is an evaluation of the contact performance between the external electrode and the internal electrode. More specifically, a conductive paste is applied to both ends of a component body having a plane size of 0.2 mm × 0.1 mm by a dip method and fired at a temperature of 720 ° C. to form an external electrode to form a static electrode. A sample to be a multilayer ceramic capacitor having an electric capacity of 10 nF was obtained. Next, the temperature of 150 ° C. was applied to the sample multilayer ceramic capacitor for 1 hour, and then the initial capacitance was measured 24 hours later. Next, the multilayer ceramic capacitor as a sample was charged at an applied voltage of 12.6 V, which was twice the rated voltage, for 5 seconds, and then allowed to stand on a metal container to discharge the electrons accumulated inside under 0 ohm. Then, the temperature of 150 ° C. was applied to the sample multilayer ceramic capacitor again for 1 hour, and the capacitance was measured after another 24 hours. The number of samples in which this volume was reduced by 5% or more from the above-mentioned initial volume was counted. In the table below, if this number is 2 or more, it is displayed as "x", if it is 1, it is displayed as "Δ", and if it is 0, it is displayed as "○".

The "fixing performance" is an evaluation of the fixing performance of the external electrode to the component body. More specifically, conductive paste is applied to both ends of a component body having a plane size of 0.2 mm × 0.1 mm by a dip method, and the mixture is fired at a temperature of 720 ° C. to form an external electrode, and then further. The external electrode was Sn-plated to prepare a sample multilayer ceramic capacitor. Next, as shown in FIG. 3, the multilayer ceramic capacitor 22 is placed on the substrate 21 in a state where the component main body 23 of the multilayer ceramic capacitor 22 is erected, and the solder 25 is applied to the lower external electrode 24 to form the multilayer ceramic capacitor 22. It was fixed to the substrate 21. In this state, as shown by the arrow 26, the upper external electrode 27 was pushed sideways. The destruction mode caused by this sideways push,
(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 4 categories. For 10 samples, if even one of them encountered the destruction mode of (3), it was judged to be defective and marked with "x" 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. 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. In Experimental Example 1, the thickness of the external electrode after firing was set to 30 μm on the end face of the component body.

In Table 1, the samples 1, 2 and 4 satisfy the conditions that the copper powder has a "particle diameter" of 300 nm or less and a "particle diameter / crystallite diameter" of more than 1.0 and 3.8 or less. It is . "Blister", "contact performance" and "sticking performance" are evaluated as "○".

On the other hand, in Sample 3, since the "particle diameter / crystallite diameter" of the copper powder is 10.0, which exceeds 3.8, the "blister" is evaluated as "x".

Further, in Sample 5, since the "particle diameter / crystallite diameter" of the copper powder is 6.0, which exceeds 3.8, the "blister" is evaluated as "x". In sample 5, the "particle diameter" of the copper powder is 300 nm, which is larger than 100 nm in the case of sample 2, so that the "sticking performance" is further evaluated as "x".

Further, in sample 6, the "particle diameter" of the copper powder is 500 nm, which exceeds 300 nm, and the "particle diameter / crystallite diameter" is 5.0, which exceeds 3.8. Therefore, "blister" and "contact performance". And "sticking performance" is evaluated as "x".

Further, in the sample 7, the condition that the "particle diameter / crystallite diameter" of the copper powder exceeds 1.0 and is 3.8 or less is satisfied, but the "particle diameter" is 500 nm, which exceeds 300 nm. , "Blister", "contact performance" and "sticking 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. 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 body was set to be 50 μm, which was thicker than that in Experimental Example 1. It is presumed that the thicker 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. Further, among the samples 11 to 18, for the samples 11 to 13 and 15 to 18 excluding the sample 14, the "particle diameter / crystallite diameter" of the copper powder is said to be more than 1.0 and 3.8 or less. The conditions are satisfied and it is within the scope of the present 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 or more and 2.0 or less, which are considered to be 3.3 and 3.0, respectively.

From this, as the thickness of the external electrode becomes thicker, the risk of blister failure increases. Therefore, the "particle diameter / crystallite diameter" of the copper powder is set to a range of more than 1.0 and 3.8 or less. It can be seen that it is desirable to narrow the range to 1.1 or more and 2.0 or less.

That is, in the samples 12, 13, 15, 16 and 18 in which the "particle diameter / crystallite diameter" of the copper powder was narrowed to the range of 1.1 or more and 2.0 or less, the thickness of the external electrode was as thick as 50 μm. However, the evaluation of "Blister" 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. Further, in Experimental Example 3, as in the case of Experimental Example 1, the thickness of the external electrode after firing was set to 30 μm on the end face of the component body.

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 in the range of 5 to 35% by volume as shown in “Glass ratio” in Table 3.

First, paying attention to the "particle size" of the copper powder, the samples 29 to 31 are outside the scope of the present invention in that they are 500 nm, which exceeds 300 nm. Therefore, at least one of "contact performance" and "sticking performance" is evaluated as "x".

On the other hand, the samples 21 to 28 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" of 1.1 or more and 2.0 or less. It meets the condition that there is. Although not shown in Table 3, no blister defect occurred in these samples 21 to 28.

However, among the samples 21 to 28, only the samples 22 to 24, 26 and 27 have "○" in each evaluation of "contact performance" and "sticking performance". Focusing on the "glass ratio" in Samples 22-24, 26 and 27, the "glass ratio" is in the range of 10-25% by volume.

On the other hand, in the samples 21 and 25 in which the "glass ratio" is less than 10% by volume and is 5% by volume and 7% by volume, respectively, the evaluation of "fixing performance" is "x". The evaluation of "fixing performance" was "x" because the "glass ratio" was relatively low, but even in sample 25 with 7% by volume, where the "glass ratio" was higher than 5% by volume of sample 21, " It is presumed that the "sticking performance" was evaluated as "x" because the "particle size" of the copper powder was 300 nm, which was larger than 100 nm of the sample 21.

Further, in the sample 28 in which the "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 in which the "glass ratio" is also 35% by volume, the evaluation of "contact performance" is "◯". This is not a problem if the "particle size" of the copper powder is as small as 100 nm as in sample 24 when the "glass ratio" is set to 35% by volume, which is relatively large, but there is no problem as in sample 28. It is shown that there is a concern that the "contact performance" may deteriorate when the "particle size" of the above is relatively large as 300 nm. From a different point of view, it is shown that even if the "glass ratio" is relatively large at 35% by volume, good contact performance can be obtained by reducing the "particle diameter" of the copper powder to 100 nm.

As described above, as the chip-type ceramic electronic component to which the conductive paste according to the present invention is applied to form an external electrode, a laminated ceramic capacitor has been mainly exemplified and described, but the conductive paste is another chip-type ceramic electronic component. It can also be used for forming an external electrode.

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

Claims (7)

A conductive paste for forming external electrodes in chip-type ceramic electronic components.
Contains copper powder and glass powder
The copper powder has a particle diameter of 300 nm or less, a particle diameter / crystallite diameter of 1.1 or more and 2.0 or less.
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.
Conductive paste. The conductive paste according to claim 1, wherein the crystallite diameter of the copper powder is 50 nm or more. The inside of the powder particles of the copper powder does not contain impurities, or when chlorine is contained, the amount of chlorine ions is 0.01% by mass or less, and when sulfur is contained, the amount of sulfur is 0.002% by mass. The conductive paste according to claim 1 or 2 , which contains less than%. The conductive paste according to any one of claims 1 to 3 , wherein the copper powder is composed of spherical powder particles. The conductive paste according to any one of claims 1 to 4 , wherein the volume ratio of the glass powder to the total volume of the copper powder and the glass powder is 10% by volume or more and 25% by volume or less. The conductive paste according to any one of claims 1 to 5 , wherein the glass powder has a particle size of 1.0 μm or less. The conductive paste according to any one of claims 1 to 6 , wherein the glass powder is made of B—Si based glass.