JPH09282935A - Silver-plated copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide inexpensive conductive paste excellent in conductivity and migration resistance by setting a ratio of silver forming a porous coating film to copper powder within a predetermined range. SOLUTION: In silver-plated copper powder in which a porous silver coating film is formed on copper powder, a ratio of the silver forming the porous coating film to the copper powder is 5-30wt%. In this case, a particle size of the silver-plated copper powder is increased by 5-100% and a specific surface area is increased by 50-300%, respectively, with respect to the copper powder before plating. An average particle diameter of the copper powder ranges within 1-50μm, 1-30μm or 1-10μm. Consequently, a using quantity of expensive silver powder can be reduced. Furthermore, it is possible to provide conductive paste excellent in conductivity and migration resistance.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a silver-plated copper powder suitable as a conductive paste for forming an electric circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a wiring conductor such as a wiring board or an electronic component, Japanese Patent Laid-Open Publication No. 6-325617
As shown in JP-A-6-333417, gold,
There is a method in which a conductive metal powder such as silver, palladium, copper, or aluminum is used as a conductive powder, and a conductive paste made into a paste by adding a binder and a solvent such as resin or glass frit to this is applied or printed. Is commonly known. Since gold is extremely expensive among various conductive metal powders, silver is often used as a conductive powder in fields where high conductivity is required and copper is used as a conductive powder in other fields.

However, silver is expensive next to gold and palladium, and when a direct current voltage is applied in the presence of moisture, silver electrodeposition called migration occurs on electrodes or wiring conductors, and the electrodes or the wirings are electrically connected. The serious problem of short circuiting occurs.

On the other hand, copper is inexpensive and relatively resistant to migration, but when heating the conductive paste,
There is a problem that an oxide film is formed on the surface of the copper particles by air and oxygen in the binder to deteriorate the conductivity. For this reason, measures such as applying a moisture-proof coating to the surface of the conductor, corroding the conductive paste, and adding an antioxidant have been investigated, but sufficient effects have not been obtained.

Therefore, Japanese Patent Laid-Open No. 56-8892 proposes to use silver-plated copper powder as a conductive powder for a conductive paste. Sex paste has hardly been put to practical use.

An electroless plating method is used as a method for plating fine powder with silver. The electroless plating method includes a displacement plating method involving elution of metal ions to be plated into a plating solution, and a plating solution. There is a chemical reduction plating method in which a metal salt therein receives electrons from a reducing agent in a plating solution to form a metal film. However, when the surface of the metal to be plated is completely covered with the plating film, the displacement plating method cannot be used to form a thick film, and the film quality is poor, so it is practically put to practical use in industry. However, the chemical reduction plating method is generally called electroless plating.

On the other hand, also in the chemical reduction plating method, the adjustment and control of the so-called plating solution, in which a soluble reducing agent, a pH adjusting agent, a stabilizing agent of the plating solution and the like are essential materials, are complicated, and are several microns or submicrons. It is difficult to uniformly form a plating film on the fine powder with good adhesion. The heat-treated conductive paste containing a large amount of spherical silver-plated copper powder having a small specific surface area has a problem of high resistance.

[0008]

SUMMARY OF THE INVENTION The invention according to claim 1 provides a silver-plated copper powder for obtaining a conductive paste at low cost and having excellent conductivity and migration resistance. In addition to the effect of the invention described in claim 1, the invention described in claim 2 provides a silver-plated copper powder for obtaining a conductive paste having further excellent conductivity.

[0009]

The present invention relates to a silver-plated copper powder obtained by forming a porous silver coating on the surface of copper powder. Further, the present invention relates to the silver-plated copper powder according to the first aspect of the invention, wherein the ratio of silver forming the porous film is 5 to 30% by weight based on the copper powder.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The coating amount of silver is 5 to copper powder.
The range of 30 wt% is preferable, the range of 10 to 25 wt% is more preferable, and the range of 15 to 20 wt% is further preferable. If it is less than 5% by weight, there is much exposed copper surface, so there is little effect of silver plating. On the other hand, if it exceeds 30% by weight, the agglomeration of powder particles becomes extremely large, resulting in poor conductivity and printability. At the same time, it tends to be difficult to manufacture at low cost.

The particle size of the silver-plated copper powder is 5 to 100% larger than that of the copper powder before plating, and the specific surface area is 50.
A size of ˜300% is preferable for forming a porous silver film.

The average particle size of the copper powder used in the present invention is 1 to 50.
The range of μm is preferable, the range of 1 to 30 μm is more preferable, and the range of 1 to 10 μm is further preferable. If it is less than 1 μm, it takes a long time to pulverize the powder, so that the powder price increases, and precipitation or filtration after plating tends to be troublesome. On the other hand, if it exceeds 50 μm, the resistance and printability tend to be significantly deteriorated. The shape of the copper powder is not particularly limited, but it is preferable to use a copper powder whose copper surface is not oxidized and which is free of oils and fats.

The silver plating is preferably performed by a displacement plating method because a large amount of a porous silver film having an apparent density of ³ to 9.5 g / cm ³ can be plated. In the displacement plating method, it is preferable to adjust the plating at a high speed by, for example, pouring a plating solution containing a predetermined amount of silver all at once. By plating by such a method, a large amount of porous silver film having an apparent density of ³ to 9.5 g / cm ³ can be plated.

[0014] Note that silver has an apparent density preferably in the range of 3~9.5g / cm ^3, more preferably in the range of 4~8g / cm ^3,
More preferably, it is in the range of ^{5 to} 7 g / cm ³ . If the apparent density is less than 3 g / cm ³ , the conductivity tends to deteriorate, whereas if it exceeds 9.5 g / cm ³ , a porous silver coating cannot be formed, and the conductivity and migration resistance are reduced. It tends to be impossible to improve.

In the present invention, the apparent density ρ (g / cm ³ ) of silver of the silver-plated copper powder is obtained from the following formula, where the radius of the copper portion of the silver-plated copper powder is r ′ (cm). The radius of the silver-plated copper powder is R (cm), the radius of the base copper powder before plating is r (cm), and the silver plating amount is C (% by weight). In addition, C in the above is obtained by dissolving 1 g of silver-plated copper powder in nitric acid and performing chemical quantitative analysis or atomic absorption analysis, and the radius of the silver-plated copper powder is R and the radius r of the base copper powder before plating is r.
Is determined by selecting 50 or more from the SEM photograph, measuring the particle size of each particle, and calculating the average value thereof.

When the plating amount is C% by weight,

[Equation 1] Also, since the number of moles of eluted copper is equal to the number of moles of plated silver,

[Equation 2] By substituting C, r and R into the equations of the equations 1 and 2, r ′ and ρ can be obtained.

In addition to the above silver-plated copper powder, the conductive paste is a binder such as epoxy resin, phenol resin, unsaturated polyester resin, hexamethylenetetramine, butyl cellosolve, ethylene carbitol, carbitol acetate, etc. and necessary. Depending on the requirement, flaky silver powder, a surfactant, a copper antioxidant, etc. are added and uniformly mixed. The content of the binder and the solvent is preferably 10 to 30% by weight of the binder and 10 to 30% by weight of the solvent with respect to the conductive paste. Further, the content of the silver-plated copper powder is preferably in the range of 40 to 80% by weight from the viewpoint of the resistance and economy of the conductor with respect to the conductive paste.

[0018]

Embodiments of the present invention will be described below. Example 1 The average particle size is 5.5 μm, and the specific surface area according to the BET method is 0.
Put 2m ² / g of copper powder (Nippon Atomize Co., Ltd.) in the plating bath, wash with stirring with water, and then replace the washed water with fresh water to prevent the copper powder from precipitating. With sufficient stirring, when the added silver is all displacement plated, 20% by weight of silver is plated with respect to the copper powder.
20 g of CN and 40 g of NaCN are dissolved in 1 liter of water)
Was thrown in at a stretch. After 30 minutes, stirring was stopped when free silver ions were no longer detected in the liquid, the waste liquid was removed by decantation, and the product was further washed and dried to obtain a silver-plated copper powder. The apparent density of the silver coating of the obtained silver-plated copper powder was 3 g / cm ³ , the silver content was 19% by weight with respect to the copper powder, the average particle size was 6.5 μm, and the specific surface area was 0.6 m ² / It was g. 50 parts by weight of the above silver-plated copper powder, 50 parts by weight of flake-shaped silver powder having an average particle size of 8.5 μm (trade name TCG-1 manufactured by Tokuriki Kagaku Kenkyusho), novolac type phenol resin (Gunei Chemical Industry Co., Ltd.) Made, product name PS-2607) 15
Parts by weight and 15 parts by weight of butyl cellosolve were added and uniformly mixed to obtain a conductive paste.

Then, the conductive paste was printed on a 1.6 mm-thick paper phenol laminate through a 200-mesh screen to form a test pattern having a width of 0.5 mm and a length of 100 mm. Heat treatment was performed for a minute. The specific resistance of the obtained paste cured product was 95 μΩcm. On the other hand, separately from the above, 6 pieces of the conductive paste are printed on the slide glass so that the wiring conductors having a width of 2 mm and a length of 20 mm are spaced from each other by 3 mm, and the electrodes are heat-treated in the same manner as above. Obtained. Next, 0.05 cc of ion-exchanged water was dropped between the electrodes, a direct current voltage of 10 V was applied, and the elapsed time and leakage current were measured to evaluate migration resistance. As a result, the time required for the leakage current of 200 μA to flow was 30 minutes.

Example 2 The average particle size is 45 μm, and the specific surface area according to the BET method is 0.0.
Using 7 m ² / g of copper powder (manufactured by Japan Atomized Co., Ltd.), the silver plating amount (theoretical value) was set to 5% by weight with respect to the copper powder, and the same steps as in Example 1 were followed to obtain silver. The apparent density of the coating is 4.5g / cm ³ , and the silver content is 5% by weight with respect to the copper powder.
(Measured value), average particle size is 50 μm, and specific surface area is 0.1
1 m ² / g of silver-plated copper powder was obtained. 50 of the above silver-plated copper powder
50 parts by weight of flake-shaped silver powder having an average particle size of 8.5 μm (manufactured by Tokuriki Kagaku Kenkyusho, trade name TCG-1), novolac type phenol resin (manufactured by Gunei Chemical Industry Co., Ltd., trade name P)
S-2607) 12 parts by weight and butyl cellosolve 10 parts by weight were added and uniformly mixed to obtain a conductive paste.

Then, the conductive paste was printed on a 1.6 mm-thick paper phenol laminate used in Example 1 through a 150-mesh screen to form a test pattern having a width of 2 mm and a length of 50 mm, which was then exposed to the atmosphere. At 150 ° C. for 45 minutes. The specific resistance of the obtained paste cured product is 12
It was 0 μΩcm. Further, an electrode was formed on the slide glass with the conductive paste in the same manner as in Example 1, and the migration resistance was evaluated. As a result, the time required for the leakage current of 200 μA to flow was 15 minutes.

Example 3 The average particle size was 5.5 μm, and the specific surface area according to the BET method was 0.
Using 2 m ² / g of copper powder (manufactured by Nippon Atomize Co., Ltd.), the plating amount (theoretical value) was set to 30% by weight with respect to the copper powder, and the same process as in Example 1 was followed to obtain silver The apparent density of the coating is 5g / cm ³ , and the silver content is 28% by weight based on the copper powder.
(Actually measured value), the average particle size is 9.5 μm, and the specific surface area is 0.
9 m ² / g of silver-plated copper powder was obtained. 50 of the above silver-plated copper powder
50 parts by weight of flake-shaped silver powder having an average particle size of 8.5 μm (manufactured by Tokuriki Kagaku Kenkyusho, trade name TCG-1), novolac type phenol resin (manufactured by Gunei Chemical Industry Co., Ltd., trade name P)
S-2607) 12 parts by weight and butyl cellosolve 10 parts by weight were added and uniformly mixed to obtain a conductive paste.

Then, the conductive paste was passed through a screen of 200 mesh on the paper phenol laminate having a thickness of 1.6 mm used in Example 1 and having a width of 0.5 mm and a length of 10 mm.
Printed on a 0mm test pattern and 4 at 150 ℃ in air.
Heat treatment was performed for 5 minutes. The specific resistance of the obtained paste cured product was 85 μΩcm. Further, an electrode was formed on the slide glass with the conductive paste in the same manner as in Example 1, and the migration resistance was evaluated. As a result, 200 μA
It took 20 minutes for the leakage current to flow.

Example 4 The average particle size is 3.5 μm, and the specific surface area by the BET method is 0.
Put 3m ² / g of copper powder (Nippon Atomize Co., Ltd.) into the plating bath, wash with stirring with water, and then replace the washed water with fresh water to prevent precipitation of copper powder. With sufficient stirring, when the added silver is all displacement plated, 15% by weight of silver is plated with respect to the copper powder.
20 g of g (CN) _{2 and} 20 g of NaCN were dissolved in 1 liter of water) were added over 30 minutes. After 30 minutes, stirring is stopped when free silver ions are no longer detected in the solution,
The waste liquid was removed by decantation, further washed and dried to obtain silver-plated copper powder. The apparent density of the silver coating of the obtained silver-plated copper powder was 9.5 g / cm ³ , the silver content was 15% by weight relative to the copper powder, the average particle size was 5.5 μm, and the specific surface area was 0.9 m. It was ² / g. 50 parts by weight of the above silver-plated copper powder, 50 parts by weight of flake-shaped silver powder having an average particle size of 8.5 μm (trade name TCG-1 manufactured by Tokuriki Kagaku Kenkyusho), novolac type phenol resin (Gunei Chemical Industry Co., Ltd.) Made, product name PS
-2607) 12 parts by weight and butyl cellosolve 10 parts by weight were added and uniformly mixed to obtain a conductive paste.

Then, the conductive paste is applied to a thickness of 1.6 mm.
A test pattern having a width of 0.5 mm and a length of 100 mm was printed on a paper-phenolic laminated sheet of No. 3 through a 200-mesh screen and heat-treated at 150 ° C. for 45 minutes in the atmosphere. The specific resistance of the obtained paste cured product was 85 μΩcm. Further, an electrode was formed on the slide glass with the conductive paste in the same manner as in Example 1, and the migration resistance was evaluated. As a result, the time required for the leakage current of 200 μA to flow was 35 minutes.

Comparative Example 1 100 parts by weight of flake-shaped silver powder having an average particle size of 8.5 μm (manufactured by Tokuriki Kagaku Kenkyusho, trade name TCG-1) was added to a novolac type phenol resin (manufactured by Gunei Chemical Industry Co., Ltd. Name PS-
2607) 12 parts by weight and butyl cellosolve 10 parts by weight were added and uniformly mixed to obtain a conductive paste. Then, the conductive paste was passed through a 200-mesh screen to a width of 0.5 on a paper-phenolic laminate having a thickness of 1.6 mm.
A test pattern having a size of 100 mm and a length of 100 mm was printed, and heat-treated in air at 150 ° C. for 45 minutes. The specific resistance of the obtained paste cured product was 85 μΩcm. Further, an electrode was formed on the slide glass with the conductive paste in the same manner as in Example 1, and the migration resistance was evaluated. As a result, the time required for the leakage current of 200 μA to flow was as short as 1 minute.

Comparative Example 2 The average particle size was 5.5 μm, and the specific surface area according to the BET method was 0.
Put 2m ² / g of copper powder (Nippon Atomize Co., Ltd.) in the plating bath, wash with stirring with water, and then replace the washed water with fresh water to prevent the copper powder from precipitating. With sufficient stirring, when the added silver is all displacement plated, 20% by weight of silver is plated with respect to the copper powder.
20 g of CN and 40 g of NaCN are dissolved in 1 liter of water)
Was slowly added over 1 hour. Then, the stirring was stopped, the waste liquid was removed by decantation, and further washed and dried to obtain a silver-plated copper powder. The actual density of the silver coating of the obtained plating powder was 10 g / cm ³ , the silver content was only 13% by weight with respect to the copper powder, the average particle diameter was 6.0 μm and the specific surface area was 0.25 m. It was ² / g. 50 parts by weight of the above silver-plated copper powder, flaky silver powder having an average particle size of 8.5 μm (TCG-1 manufactured by Tokuriki Kagaku Kenkyusho)
50 parts by weight, 15 parts by weight of novolac type phenol resin (trade name PS-2607 manufactured by Gunei Chemical Industry Co., Ltd.) and 15 parts by weight of butyl cellosolve were added and uniformly mixed to obtain a conductive paste.

Then, the conductive paste is applied to a thickness of 1.6 mm.
A test pattern having a width of 0.5 mm and a length of 100 mm was printed on a paper-phenolic laminate of No. 1 through a 200-mesh screen and heat-treated in the air at 150 ° C. for 45 minutes. The specific resistance of the obtained paste cured product was as high as 200 μΩcm. Further, an electrode was formed on the slide glass with the conductive paste in the same manner as in Example 1, and the migration resistance was evaluated. As a result, the time required for the leakage current of 200 μA to flow was as short as 5 minutes.

Comparative Example 3 The average particle size was 5.5 μm, and the specific surface area according to the BET method was 0.
Put 2m ² / g of copper powder (Nippon Atomize Co., Ltd.) in the plating bath, wash with stirring with water, and then replace the washed water with fresh water to prevent the copper powder from precipitating. With sufficient stirring, 40% by weight of silver is plated with respect to the copper powder when all of the added silver is displacement plated.
20 g of CN and 40 g of NaCN are dissolved in 1 liter of water)
Was thrown in at a stretch. After 20 minutes, the stirring was stopped when free silver ions were still detected in the solution, the waste solution was removed by decantation, and further washed and dried to obtain silver-plated copper powder. The apparent density of the silver coating of the obtained silver-plated copper powder was 2.5 g / cm ³ , the silver content was 35% by weight with respect to the copper powder, the average particle size was 13 μm, and the specific surface area was 0.9 m ² / It was g. A conductive paste was obtained through the same steps as in Example 1 below. The specific resistance of the obtained paste cured product is 190 μΩ
cm. As a result of evaluating the migration resistance by the same method as in Example 1, the time required for the leakage current of 200 μA to flow was 10 minutes.

[0030]

The silver-plated copper powder according to claim 1 can reduce the amount of expensive silver powder used, and can provide a conductive paste having excellent conductivity and migration resistance. The silver-plated copper powder according to claim 2 has the effect of claim 1, and can provide a conductive paste having excellent conductivity.

Claims (2)

[Claims] 1. A silver-plated copper powder obtained by forming a porous silver coating on the surface of copper powder. 2. The silver-plated copper powder according to claim 1, wherein the proportion of silver forming the porous film is 5 to 30% by weight based on the copper powder.