JP2003105402A - Copper powder for conductive paste, conductive paste using the copper powder and chip component containing conductive body using the conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain copper powder which allows a low temperature baking property required for the baking manufacture of a conductive body of chip component using a conductive paste which is produced by using the copper powder and is made lower in viscosity when being fabricated into the conductive paste. SOLUTION: In this copper powder which is used for production of conductive paste and has a surface oxidized layer, weight accumulative particle size D50 according to laser diffraction scattering type particle size distribution measurement method is 0.05 μm to 10 μm, the value of (SD/D50 )×100 which is a relation between D50 and standard deviation SD of particle size distribution measured by the laser diffraction scattering type particle size distribution measurement method is <=28 and the oxygen content of the copper powder is 0.5 wt.% to 3.0 wt.%. This copper powder is produced in such a manner that copper powder is subjected to heating treatment in the air or in an environment enhanced in oxygen partial pressure, the oxidized layer is formed on the surface of powder particle constituting the copper powder, the copper powder formed with the oxidized layer is subjected to re-powdering treatment, thereby the surface of powder particle is flattened and the powder particle in the state of aggregated state is separated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a copper powder for conductive paste and a conductive paste using the copper powder.

[0002]

2. Description of the Related Art Conventionally, copper powder has been widely used as a raw material for conductive paste. Because of their ease of handling, conductive pastes have been used in a wide range of fields from experimental use to electronic industry applications.

[0003]

2. Description of the Related Art Conventionally, an external electrode of a ceramic capacitor, which is a typical chip component, is formed by forming a paste of copper powder and glass frit with a binder resin, applying the paste onto a ceramic, and removing the binder resin by heating. Further, this has been sintered and used as an electrode. Therefore, the copper powder used here has been required to have a sintering characteristic that powder particles of the copper powder are easily sintered during the sintering process.

[0004] In order to improve the sintering characteristics of the copper powder, it has been found from the study by the present inventors that an appropriate oxide layer should be provided on the surface of the copper powder particles. Therefore, a method of forming a certain amount of oxide film on the surface of the copper powder particles has been studied because it enables sintering in a low temperature range. If an oxide layer is to be formed on the surface of the copper powder particles as described above, the oxide film can be easily formed by heating in the air most simply.

On the other hand, since the copper powder used as described above is once processed into a conductive paste and used, it has the property of being capable of properly maintaining the viscosity, which is the quality of the conductive paste. Is required. That is, the conductive paste has been required to have low viscosity. It has been conventionally said that it is preferable to prevent the formation of an oxide film on the surface of the copper powder particles as much as possible as a method of applying the copper powder in view of merely lowering the viscosity of the conductive paste. Then, in order to prevent the surface of the copper powder particles from being oxidized, surface-treated copper powder that has been treated with a fatty acid oleic acid as a surface treatment agent has been used.

[0006]

However, as is clear from the above description, the copper powder having the oxide layer on the surface of the powder has excellent sintering characteristics at low temperature, but is processed into a conductive paste. It has the drawback of high viscosity. On the other hand, the surface-treated copper powder as described above lacks sintering characteristics at low temperatures, but can reduce the viscosity when processed into a conductive paste. That is, the reality is that there is no copper powder that can achieve both excellent low-temperature sintering characteristics and low viscosity of the conductive paste.

[0007] Generally, if the oxide layer of copper powder is left as it is, the resistance value increases and the electrical conductivity is deteriorated. Therefore, at the manufacturing site of ceramic capacitors, reduction treatment is performed in high-temperature reducing atmosphere gas in order to finally reduce the oxide layer, but there is a certain limit for reducing the surface of strongly oxidized copper powder. However, this is not preferable because it leads to an increase in manufacturing cost. Accordingly, when the conductive paste is sintered and the copper powder does not need to be heated at a high temperature, it is not necessary to grow an extra oxide layer on the surface of the powder particles of the copper powder.

Further, if the initial paste viscosity when processed into a conductive paste is high, the paste viscosity may change over time and increase in viscosity, making it difficult to handle at the manufacturing site and processed into a conductive paste. After that, it is difficult to store for a long time thereafter, and quality control as a conductive paste used for manufacturing electronic parts and the like, and management for quality maintenance become complicated.

Therefore, it has been desired in the market to supply copper powder capable of reducing the above-mentioned sintering characteristics at low temperature and reducing the viscosity when processed into a conductive paste.

[0010]

The inventors of the present invention have, as a result of diligent research, found that the invention described below can achieve both low-temperature sintering characteristics and low viscosity when processed into a conductive paste. This made it possible to provide copper powder and the like.

According to a first aspect of the present invention, in a copper powder having a surface oxide layer used for producing a conductive paste, a weight cumulative particle diameter D ₅₀ measured by a laser diffraction scattering type particle size distribution measurement method is 0.05 μm to 10 μm, and a laser is used. The value of (SD / D ₅₀ ) × 100, which is a relational expression with the standard deviation SD of the particle size distribution measured by the diffraction scattering type particle size distribution measuring method, is 28 or less, and the oxygen content of the copper powder is 0.5 wt% ~
The content of the copper powder is 3.0 wt% and is used as a conductive paste copper powder for forming a conductor of a chip component.

The characteristics of the copper powder for a conductive paste according to the present invention are that the weight cumulative particle diameter D ₅₀ by the laser diffraction / scattering particle size distribution measuring method is 0.05 μm to 10 μm, and the laser powder / scattering particle diameter of the copper powder is Standard deviation SD of particle size distribution measured by a distribution measuring method and weight cumulative particle size D ₅₀
The value of (SD / D ₅₀ ) × 100, which is a relational expression with
Being the following values, the oxygen content of the copper powder is 0.5
It is characterized by having three requirements, that is, wt% to 3.0 wt%. Satisfying these three requirements is a necessary element for achieving both low temperature sinterability and low viscosity when processed into a conductive paste, as copper powder for a conductive paste used for forming a conductor of a chip component. is there.

The reason why the above three requirements are required will be described below. The first requirement is that the weight cumulative particle diameter D ₅₀ by the laser diffraction / scattering particle size distribution measurement method is 0.
05 μm to 10 μm ”. Considering this from the aspect of the viscosity of the conductive paste used when forming the conductor of the chip component, when the weight cumulative particle diameter D ₅₀ of the copper powder is less than 0.05 μm, the constituent resin of the conductive paste is carefully devised. However, the viscosity of the conductive paste is likely to increase rapidly, and the paste management in actual operation becomes complicated and complicated, which is not appropriate. Further, while the electrode of the ceramic capacitor, although the it is required that the surface state after the completion of the firing process is smooth, the weight cumulative particle diameter D ₅₀
If the value exceeds 10 μm, the electrode surface after firing cannot have the smoothness required in the market, and it becomes impossible to form a fine circuit or the like.

In the present specification, the weight cumulative particle size is measured by the laser diffraction / scattering particle size distribution measuring method by mixing 0.1 g of copper powder with a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by San Nopco). , An ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Seisakusho) for 5 minutes, and then a laser diffraction / scattering particle size distribution analyzer Mic
ro Trac HRA 9320-X100 type (Le
eds + Northrup Co.).

The second requirement is that "copper powder laser
Standard of particle size distribution measured by the folding scattering type particle size distribution measurement method
Deviation SD and weight cumulative particle size D_FiftyIs a relational expression with (SD
/ D _Fifty) × 100 value is 28 or less ”
is there. Standard deviation SD of particle size distribution and weight cumulative particle size D_FiftyWhen
Is the relational expression of (SD / D_Fifty) × 100 is the standard
The deviation SD itself is an index indicating the spread of the measured distribution.
Therefore, it can be said that this value is the central value of the weight cumulative particle size D
_FiftyCan be said to have been normalized by the value of
D_FiftyIt means the spread of particle size distribution based on the value of
Of. Therefore, this (SD / D_Fifty) × 100 value
Is larger, it is a copper powder with a broad particle size distribution.
The smaller the value, the sharper the particle size distribution becomes.
It approaches the powder.

The viscosity of the conductive paste produced by using the copper powder is easily affected by the particle size distribution of the copper powder, and as the particle size distribution becomes broader, the viscosity tends to increase, and it becomes difficult to control the viscosity of the conductive paste. . Therefore, the inventors of the present invention
As a result of diligent examination in relation to the oxygen content that facilitates sintering of the copper powder particles described below, this (SD
It has been found that if the value of / D ₅₀ ) × 100 is not 28 or less, it is impossible to suppress the increase in viscosity of the conductive paste and at the same time to improve the sinterability of the powder particles.
That is, when the value of (SD / D ₅₀ ) × 100 exceeds 28, even if the oxygen content is within the range described below, the viscosity stability of the conductive paste is lacking and the conductive paste is thickened. Is easier to do.

The third requirement is that the oxygen content of the copper powder is 0.5 wt% to 3.0 wt%. That is, in the case of the copper powder having the above-mentioned particle size and particle size distribution, if the oxygen content is less than 0.5 wt%, the sintering of the powder particles cannot be facilitated. Sintering at a higher temperature than necessary is required. On the other hand, the oxygen content is 3.0 wt%
Even if it exceeds the above, it will be further improved by focusing only on the sintering characteristics of the powder particles, but it will significantly increase the viscosity when processed into a conductive paste, and there will be a great variation in the viscosity between production lots. It will be big.

The oxygen content referred to in the present specification is the oxygen content of the copper powder analyzed by using an EMGA-550FA model, which is an oxygen analyzer manufactured by Horiba, Ltd. It is derived from the oxide layer formed on the surface of the. Therefore, the oxygen content in the case of copper powder in which the oxide layer is not intentionally formed is at a level of 0.3 wt% or less. The surface oxide layer used in the present specification is not limited to a state in which the surface of copper powder particles is coated with a uniform thickness, and is used as a concept including a case of non-uniform thickness. There is.

For the reasons described above, among the three requirements,
If even one requirement is not satisfied, the effect of improving the sintering characteristics of the copper powder and, at the same time, lowering the viscosity when processed into a conductive paste cannot be obtained.

Next, in claim 2, the measured specific surface area
(SSA₁) And laser diffraction scattering particle size distribution measurement method
Accumulated weight particle size D_FiftyUsing SSA_Two= 6 / (D
_FiftySpecific surface area (SSA calculated by × 8.93)_Two)When
Is the relational expression of SSA₁/ SSA _TwoIs less than 2.5
A conductor used for forming a conductor of the chip component according to claim 1.
The copper powder is provided with a surface oxide layer for an electric paste.

The specific surface area (SSA ₂ ) described here is S
SA ₂ = 6 / (D ₅₀ × 8.93). That is, the specific surface area S based on the particle volume has a relationship of S = Ψ / D obtained by dividing the correction coefficient Ψ by the representative diameter D. Therefore, in the present invention, the value of Ψ which is the correction coefficient is 6, the weight cumulative particle diameter D ₅₀ is used as the representative diameter, the true density of copper is set to 8.93 g / cm ³ , and the theoretical specific surface area (SS
A ₂ ). On the other hand, the measured specific surface area (SSA ₁ ) is 750 g of the copper powder sample at 75 ° C.
It is a specific surface area obtained as a result of measuring with the BET 1-point method using monosorb (manufactured by Kantachrome Co., Ltd.) after degassing for 10 minutes.

Therefore, the theoretical specific surface area (SSA ₂ )
Is derived on the assumption that the surface is ideally smooth, and thus the value of SSA ₂ is smaller than the value of SSA ₁ that reflects the existence of actual surface irregularities. It is natural. _Therefore, the value of SSA 1 / SSA ₂ is that a value of 1 or more and of course, the _SSA 1 /
It means that the larger the value of SSA _2, the larger the irregularities on the surface of the powder particles. The larger the unevenness of the copper powder particles, the higher the paste viscosity when processed into a conductive paste. Generally, when a surface oxide layer is formed on the copper powder particles, the surface condition is rough and fine irregularities are formed on the surface of the powder particles. Therefore,
Using conventional copper powder with oxidized surface, SSA ₁ /
When the value of SSA ₂ is measured, copper powder having a surface oxide layer having a value of 2.5 or less reduces the paste viscosity when processed into a conductive paste at a level not seen in the past. I realized that I could do it. When the conditions described in claim 1 and the conditions described in claim 2 are satisfied, more stable sintering characteristics and reduction in viscosity of the conductive paste can be achieved.

For the production of the copper powder described above, it is preferable to employ the method described in claim 3. That is, an oxide layer is formed on the surface of the powder particles forming the copper powder, and the copper powder having the oxide layer formed thereon is subjected to a disintegration treatment to smooth the surface of the powder particles and the powder particles in an agglomerated state. Is a method for producing a copper powder.

Here, the formation of the oxide layer on the surface of the powder particles constituting the copper powder is carried out by heating the copper powder in the air or in an atmosphere with an increased oxygen partial pressure, or by a solution. It is desirable to adopt the wet oxidation method in the above. In these methods, the oxide layer formation by this heat treatment can easily form a relatively uniform and smooth oxide layer on the powder particle surface of the copper powder as compared with the wet oxidation method in which the reaction rapidly proceeds, and It is more preferable because the thickness of the oxide layer can be easily controlled.

When the surface of the copper powder is to be oxidized by heating, oxygen in the atmosphere and copper on the surface of the powder particles react actively at the start of heating to form a copper oxide layer. When the whole is covered with copper oxide, the growth of the oxide layer changes at a slow rate. This is because the growth of the oxide layer depends on the rate at which oxygen diffuses in the oxide layer already formed on the surface, and the growth rate is controlled by diffusion rate control. Therefore, if a certain amount of oxide film is completed, except for the case where heating is performed for an extremely long time ignoring the manufacturing cost and productivity, it becomes difficult to form more oxide film. Even from such a manufacturing meaning, the upper limit of the oxygen content described in claim 1 is 3.0 wt.
If it exceeds%, it will increase the production cost.

The copper powder before the heat treatment is often agglomerated to form a secondary structure, but the copper powder having the oxide layer formed by the heat treatment as described above is heated by the heat treatment. Depending on the process, the powder particles tend to be further aggregated. When the conductive paste is manufactured using copper powder, the paste viscosity tends to increase as the state of aggregation progresses. Since the oxide layer formed on the surface of the powder particles is in a rough state with irregularities, if it is used as it is, the viscosity of the conductive paste will be increased. The disintegration process is performed to eliminate this state. The disintegration treatment means that the powder in the agglomerated state is separated into individual powder particles.

For the purpose of simply performing the disintegration work, as means for performing the disintegration, a high energy ball mill, a high speed conductor collision type air flow type crusher, an impact type crusher, a gauge mill, a medium stirring type mill, It is possible to use various things such as a high water pressure type pulverizer. However, considering that the viscosity of the conductive paste using the copper powder is reduced as much as possible, it is required to make the specific surface area of the copper powder as small as possible. Therefore, even if disintegration is possible, the disintegration method should not damage the surface of the powder particles during the disintegration and increase the specific surface area. In particular,
This is an important point in the case of copper powder in which an oxide layer is intentionally formed.

Based on such recognition, the inventors of the present invention have conducted intensive studies, and as a result, have come up with the following two disaggregation methods. What is common to these two methods is to minimize the contact of the copper powder particles with the inner wall of the device, the stirring blade, the part such as the grinding medium, and the agglomerated powder particles collide with each other. In addition, it is a method that is suitable for disintegration. That is, it should not damage the surface of the powder particles by contacting the inner wall portion of the apparatus, the stirring blade, the portion such as the grinding medium, etc., and increase the surface roughness. Then, by causing a sufficient amount of collision of the powder particles, the powder particles in the agglomerated state are disintegrated, and at the same time, a method capable of smoothing the surface of the powder particles by the collision of the powder particles is adopted.

As one method for performing the disintegration treatment, it is possible to perform a dry state of the copper powder having an oxide layer formed thereon by using a wind power circulator utilizing centrifugal force. The "wind-force circulator that uses centrifugal force" here means that air is blown and the aggregated copper powder is blown up in a circular orbit to circulate the powder. They are used to collide with each other in an air stream to perform a granulation work. At this time, it is also possible to use a commercially available wind power classifier that utilizes centrifugal force. In such a case, it is not intended for classification to the last, but the wind-powered classifier plays a role of a circulator that blows air and blows agglomerated copper powder in a circular orbit.

As another granulation method, a copper powder slurry containing copper powder having an oxide layer is produced and granulated by using a fluid mill utilizing centrifugal force. "Fluid mill using centrifugal force" here means that copper powder slurry is made to flow at a high speed so as to draw a circular orbit,
The centrifugal force generated at this time causes the aggregated powder particles to collide with each other in the solvent and is used for the disintegration work.

The above-mentioned disintegration treatment can be repeated a plurality of times as necessary, and the disintegration treatment level can be arbitrarily selected according to the required quality. The disintegrated copper powder is destroyed in the agglomerated state and has excellent dispersibility. Then, the following way of thinking was adopted to judge whether or not the disintegration process was performed well. That is, the concept of aggregation degree represented by D ₅₀ / D _IA is adopted by using the weight cumulative particle size D ₅₀ by the laser diffraction scattering type particle size distribution measurement method and the average particle size D _IA obtained by image analysis. . Then, when the value of the degree of coagulation was 1.5 or less, it could be determined that a nearly complete monodisperse state could be secured.

The cohesion degree used here is adopted for the following reasons. That is, it is considered that the value of the weight cumulative particle size D ₅₀ obtained by using the laser diffraction / scattering particle size distribution measurement method is not a direct observation of the diameter of each powder particle. The powder particles that make up most of the copper powder are not so-called monodisperse powders in which individual particles are completely separated,
This is because a plurality of powder particles are agglomerated and aggregated. It can be said that the laser diffraction / scattering particle size distribution measurement method calculates the weight-accumulated particle size by capturing the agglomerated powder particles as one particle (aggregated particle).

On the other hand, a scanning electron microscope (SE
The average particle diameter D _IA obtained by image-processing the observed image of the copper powder observed using M) is obtained directly from the SEM observed image, so that the primary particles can be reliably captured, On the other hand, the existence of the agglomerated state of powder particles is not reflected at all.

Considering the above, the inventors of the present invention
Weight cumulative particle size D measured by laser diffraction scattering particle size distribution measurement method
_FiftyAnd average particle size D obtained by image analysis_IAWith and
D _Fifty/ D_IAThe value calculated by
I decided to do it. That is, the smell of copper powder of the same lot
D_FiftyAnd D_IAAnd the values can be measured with the same accuracy.
Assuming that there is an agglomerated state,
D that reflects and in the measured value_FiftyThe value of is D_IAThan the value of
Is also considered to be a large value.

At this time, the value of D ₅₀ approaches the value of D _IA infinitely if the agglomeration state of the copper powder particles is completely eliminated, and the value of D ₅₀ / D _IA , which is the agglomeration degree, becomes 1
Will approach. It can be said that it is a monodisperse powder in which the agglomeration state of powder particles is completely eliminated when the agglomeration degree becomes 1. However, in reality, there are cases where the aggregation degree shows a value of less than 1. Theoretically, in the case of a true sphere, the value does not become less than 1, but in reality, it seems that a value of a cohesion degree of less than 1 is obtained instead of a true sphere. In addition, the image analysis of the copper powder observed using the scanning electron microscope (SEM) in this specification was carried out by using IP-1000PC manufactured by Asahi Engineering Co., Ltd.
The average particle diameter D _IA was obtained by performing circular particle analysis with 0 and the degree of overlap of 20.

As a result of the disintegration treatment as described above,
The surface of the powder particles on which the oxide layer is formed has a very smooth surface, and since the agglomeration state of the powder particles can be almost completely eliminated, copper powder with extremely high dispersibility can be obtained. This makes it possible to simultaneously achieve the above-mentioned sintering characteristics and reduction of the viscosity of the conductive paste.

The above-described copper powder having an oxide layer formed thereon is once processed into a conductive paste, and is suitable for use in forming a conductor of a chip component which is particularly required to have sintering characteristics. Therefore, in claim 4, claim 1 or claim 2
According to a fifth aspect of the present invention, there is provided a conductive paste used for forming a conductor of the chip component, and the fifth aspect provides a chip component having a conductor formed using the conductive paste of the fourth aspect.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to comparative examples through embodiments.

Therefore, first, a method of manufacturing copper powder by a wet method, which is common to the first embodiment, the second embodiment, and the comparative example, will be described. Here, 100 kg of copper sulfate (pentahydrate) is dissolved in warm water to obtain 200 at a liquid temperature of 60 ° C.
L of solution. Then, 125 liters of a 25 mass% sodium hydroxide aqueous solution was added thereto,
While maintaining the liquid temperature at 60 ° C., stirring was performed for 1 hour to form cupric oxide.

When the production of cupric oxide is completed, the liquid temperature is raised to 6
The temperature was continuously maintained at 0 ° C., and 80 liters of a glucose aqueous solution having a concentration of 450 g / l was added thereto at a constant rate over 60 minutes to produce a cuprous oxide slurry. Here, this slurry is once filtered and washed, and then warm water is added to the slurry to 320
L of reslurry.

Next, 1.5 kg of aminoacetic acid and 0.7 kg of gum arabic were added to the reslurry and stirred to keep the solution temperature at 50 ° C. To the reslurry in this state, 50 liters of hydrazine hydrate having a concentration of 20% by mass was added at a constant rate over 60 minutes to reduce cuprous oxide to form copper powder, thereby producing a copper powder slurry. This copper powder slurry is a copper powder slurry used in the second embodiment below.

Subsequently, this copper powder slurry was filtered, thoroughly washed with pure water, filtered, dehydrated and dried to obtain copper powder. The weight cumulative particle size D ₅₀ of this copper powder measured by the laser diffraction scattering type particle size distribution measurement method is 5.46 μm, and the standard deviation SD of the particle size distribution measured by the laser diffraction scattering type particle size distribution measurement method and the weight cumulative particle size D The value of (SD / D ₅₀ ) × 100, which is a relational expression with ₅₀ , is 26.3, the oxygen content of the copper powder is 0.21 wt%, and SSA ₁ /
The value of SSA ₂ was 2.8. Then, the average particle diameter _{D IA} obtained by image analysis at this stage 3.31, therefore cohesion calculated by _D 50 _{/ D I A} was 1.65.

First Embodiment: In this embodiment, the above-mentioned copper powder is put into a heating furnace and the temperature is set to 200 ° C. in an air atmosphere.
The heat treatment was carried out for 2 hours to form an oxide layer on the surface of the copper powder particles. The powder characteristics of the copper powder that has been subjected to this heat treatment are the weight cumulative particle size D measured by the laser diffraction / scattering particle size distribution measurement method.
₅₀ is 5.97 μm, which is a relational expression between the standard deviation SD of the particle size distribution measured by the laser diffraction / scattering particle size distribution measurement method and the weight cumulative particle size D ₅₀ (SD / D ₅₀ ) × 1.
The value of 00 is 28.7, the oxygen content of the copper powder is 0.63 wt%, and the value of SSA ₁ / SSA ₂ is 3.
It was 8. Then, at this stage, the average particle size D _IA obtained by image analysis is 3.34, and therefore the degree of aggregation calculated by D ₅₀ / D _IA is 1.79, indicating that the state of aggregation is progressing.

Then, the copper powder having an oxide layer formed by heat treatment was rotated at a rotational speed of 6500 using a commercially available wind classifier Turbo Classifier manufactured by Nisshin Engineering Co., Ltd.
Circulation was carried out at rpm, and the powder particles in the agglomerated state were made to collide with each other for the disintegration work.

As a result, the powder characteristics of the copper powder after the disintegration work were such that the weight cumulative particle diameter D ₅₀ by the laser diffraction scattering particle size distribution measurement method was 3.20 μm, and the laser diffraction scattering particle size distribution measurement method was used. it is a relational expression between the standard deviation SD and the weight-cumulative particle diameter D ₅₀ of the particle size distribution measured by (SD / D
The value of ₅₀ ) × 100 was 19.5, the oxygen content of the copper powder was 0.61 wt%, and the value of SSA ₁ / SSA ₂ was 1.8. All powder properties meet the requirements of the present invention. The average particle size D _IA obtained by image analysis at this stage is 3.16, and thus the aggregation degree calculated by D ₅₀ / D _IA is 1.11.
It was also confirmed that sufficient disintegration treatment was performed.

The present inventors manufactured a terpineol-based conductive paste using the copper powder obtained as described above. The terpineol-based conductive paste produced here is
The surface-treated copper powder was used in a composition of 88 parts by weight and the binder was 12 parts by weight, and these were kneaded to obtain a terpineol-based conductive paste. The binder at this time is
A composition having 93 parts by mass of terpineol and 7 parts by mass of ethyl cellulose was used. The viscosity of the terpineol-based conductive paste immediately after production is 400 Pa.
s, and the viscosity after one week was 430 Pa · s.

Furthermore, the present inventors use the terpineol-based conductive paste obtained as described above to confirm the sintering characteristics by using the same method as in the production of electrodes for ceramic capacitors. The following method was adopted. Dry film thickness of 20 μm on alumina substrate 1
A cm × 2 cm size ceramic layer plate was manufactured. Then, this ceramic layer plate was dipped in the epoxy-based conductive paste and pulled up and fired. At this time, the copper powder produced in this embodiment can be fired at a temperature of at least 650 ° C., and the surface state after firing was in a good state without any noticeable roughness.

Second Embodiment: In the present embodiment, the above-mentioned copper powder is put into a heating furnace, and heat treatment is performed at 150 ° C. for 1 hour in an atmosphere in which the oxygen partial pressure is increased to obtain copper powder particles. An oxide layer was formed on the surface. The atmosphere with an increased oxygen partial pressure was formed by using a burner heating furnace as a heating furnace and changing the combustion air-fuel ratio of the burner to create an atmosphere with an oxygen concentration of 3.28%. The powder property of the copper powder that has been subjected to this heat treatment is that the weight cumulative particle size D ₅₀ by the laser diffraction scattering type particle size distribution measurement method is 6.02 μm, and that of the particle size distribution measured by the laser diffraction scattering type particle size distribution measurement method. Standard deviation SD
And a relational expression of the weight cumulative particle diameter _{D 5 0} (SD /
The value of D ₅₀ ) × 100 is 29.1, the oxygen content of the copper powder is 2.50 wt%, and SSA ₁ / SSA ₂
Was 4.7. The average particle size D _IA obtained by image analysis at this stage is 3.33, and therefore D ₅₀
/ D cohesion calculated by _IA is 1.81, it can be seen that aggregated state is in progress.

Then, the copper powder having an oxide layer formed by the heat treatment was rotated at a rotational speed of 6500 using a commercially available wind classifier Turbo Classifier manufactured by Nisshin Engineering Co., Ltd.
Circulation was carried out at rpm, and the powder particles in the agglomerated state were made to collide with each other for the disintegration work.

As a result, the powder characteristics of the copper powder after the disintegration work were such that the weight cumulative particle diameter D ₅₀ by the laser diffraction scattering particle size distribution measurement method was 3.26 μm, and the laser diffraction scattering particle size distribution measurement method was used. it is a relational expression between the standard deviation SD and the weight-cumulative particle diameter D ₅₀ of the particle size distribution measured by (SD / D
The value of ₅₀ ) × 100 was 19.5, the oxygen content of the copper powder was 2.58 wt%, and the value of SSA ₁ / SSA ₂ was 2.1. All powder properties meet the requirements of the present invention. Then, at this stage, the average particle diameter D _IA obtained by image analysis is 3.20, and therefore the aggregation degree calculated by D ₅₀ / D _IA is 1.01.
It was also confirmed that sufficient disintegration treatment was performed.

The present inventors manufactured a terpineol-based conductive paste using the copper powder obtained in the second embodiment,
The viscosity of the conductive paste was measured. The composition and manufacturing method of the terpineol-based conductive paste manufactured here are the same as in the case of the first embodiment, so description thereof is omitted. The viscosity of the obtained terpineol-based conductive paste immediately after production was measured and found to be 320 Pa · s.

Further, the inventors of the present invention evaluated the sintering characteristics by using the same method as in the first embodiment. as a result,
The copper powder produced in this embodiment can be fired at a temperature of at least 550 ° C., and the surface state after firing was in a good state without any noticeable roughness.

Comparative Example 1: In this comparative example, the copper powder obtained by the hydrazine reduction method described above was heat treated to form an oxide layer, and the same solution as that used in the first embodiment was simply used. Grain treatment was performed. The weight cumulative particle diameter D ₅₀ of this copper powder measured by the laser diffraction / scattering particle size distribution measurement method is 3.28 μ.
m is a relational expression between the standard deviation SD of the particle size distribution measured by the laser diffraction / scattering particle size distribution measuring method and the weight cumulative particle size D _50, and the value of (SD / D ₅₀ ) × 100 is 20.
5, the oxygen content of the copper powder was 0.22 wt%, and the value of SSA ₁ / SSA ₂ was 1.5. The average particle size D _IA obtained by image analysis at this stage
Was 3.24, and therefore the aggregation degree calculated by D ₅₀ / D _IA was 1.01. That is, except for the oxygen content, the properties of the copper powder according to the present invention are satisfied.

The present inventors manufactured a terpineol-based conductive paste using this copper powder and measured the viscosity of the conductive paste. The composition and manufacturing method of the terpineol-based conductive paste manufactured here are the same as in the case of the first embodiment, so description thereof is omitted. The viscosity of the obtained terpineol-based conductive paste immediately after its production was measured and found to be 300 Pa · s. Comparing this result with the result of the above-mentioned embodiment, if only looking at the paste viscosity,
It can be seen that a very low good viscosity can be achieved.

However, the result of evaluation of the sintering characteristics using the same method as in the first embodiment shows that the copper powder used in Comparative Example 1 cannot be sintered unless the temperature is at least 800 ° C. It can be seen that higher temperatures are required compared to the two embodiments described above.

Comparative Example 2 In this comparative example, the copper powder obtained by the hydrazine reduction method described above was used for the terpineol-based conductive paste without the pulverization treatment after the heat treatment performed in the first embodiment. Was manufactured. Therefore,
Since the powder characteristics of the copper powder used for manufacturing the terpineol-based conductive paste are the same as those after the heating in the first embodiment and before the disintegration treatment, description thereof will be omitted here. That is, except for the oxygen content, the powder characteristics required for the copper powder according to the present invention are not satisfied.

The present inventors manufactured a terpineol-based conductive paste using this copper powder and measured its viscosity. The composition and manufacturing method of the terpineol-based conductive paste manufactured here are the same as in the case of the first embodiment, so description thereof is omitted. The viscosity of the obtained terpineol-based conductive paste immediately after production was measured to be 1000 P.
It was a.s. Comparing this result with the result of the above-described embodiment, it is found that the paste viscosity is extremely high, the paste viscosity cannot be reduced, and the viscosity control becomes very very difficult. .

However, as a result of evaluating the sintering characteristics by using the same method as that of the first embodiment, the copper powder used in Comparative Example 2 can be sintered at a temperature of at least 670 ° C. , Which is equivalent to the results of the two embodiments described above.

As can be seen from the above, the copper powder according to the embodiment can simultaneously achieve reduction of paste viscosity and improvement of sintering characteristics. It can be seen that the result lacks the characteristics of.

[0060]

EFFECTS OF THE INVENTION By using the copper powder having an oxide layer according to the present invention, the viscosity of the conductive paste to be manufactured can be lowered, and at the same time, the firing at a low temperature required when manufacturing an electrode of a laminated ceramic capacitor. The result is that the binding property is sufficiently satisfied. Further, since the copper powder according to the present invention is essential to reduce the roughness of the powder particle surface when the oxide layer is formed, in order to reduce the paste viscosity, the manufacturing method in which the disintegration treatment is incorporated is performed. By adopting the method, it is possible to efficiently manufacture.

Claims (5)

[Claims] 1. A copper powder having a surface oxide layer used for producing a conductive paste, wherein a weight cumulative particle diameter D ₅₀ by a laser diffraction / scattering particle size distribution measuring method is 0.05 μm to 10 μm, and a laser diffraction / scattering particle diameter. Standard deviation SD of particle size distribution measured by the distribution measurement method
The value of (SD / D ₅₀ ) × 100, which is a relational expression with
It is the following value, and the oxygen content of the copper powder is 0.5.
Copper powder for a conductive paste used for forming a conductor of a chip part, characterized in that the content of the copper powder is from wt% to 3.0 wt%. 2. Measured specific surface area (SSA ₁ ) and weight cumulative particle diameter D measured by a laser diffraction / scattering particle size distribution measurement method.
SSA is a relational expression with the specific surface area (SSA ₂ ) calculated by SSA ₂ = 6 / (D ₅₀ × 8.93) using _50.
The copper powder for a conductive paste used for forming a conductor of a chip component according to claim 1, wherein the value of ₁ / SSA ₂ is 2.5 or less. 3. An oxide layer is formed on the surface of the powder particles constituting the copper powder, and the copper powder on which the oxide layer is formed is subjected to a disintegration treatment to smooth the surface of the powder particles and bring them into an agglomerated state. A method for producing copper powder for a conductive paste according to claim 1 or 2, wherein certain powder particles are separated. 4. A conductive paste used for forming a conductor of the chip component according to claim 1. 5. A chip component containing a conductor using the conductive paste according to claim 4.