JP2002245850A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste having excellent soldering property. SOLUTION: The conductive paste contains conductive powder and binder, and for the solid portion of the conductive paste, the volume ratio of the conductive powder:the binder ranges between 45:55-79:21, and the weight ratio of the conductive powder:the binder ranges between 88:12-96.5:3.5, and a glass transition point (Tg) of the hardened conductive paste ranges between 40-80 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste which is used as an electronic component, a circuit wiring material, an electrode material and a conductive bonding material, and which can be directly soldered.

[0002]

2. Description of the Related Art A conventional conductive paste is an electronic material, 199.
As described in the October, 4th issue, paragraphs 42-46,
Conventionally, a conductive powder such as gold, silver, copper, or carbon was used, and a binder, an organic solvent, and an additive as needed were added to the powder and mixed to form a paste. Particularly in a field where high conductivity is required, gold powder or silver powder has been generally used.

[0003] Conductive pastes containing silver powder are used for forming electric circuits and electrodes of printed wiring boards, electronic components, etc. because of their good conductivity, but they can be electrolyzed in a hot and humid atmosphere. In this case, silver deposition called migration occurs in an electric circuit or an electrode, resulting in a short circuit between the electrodes or the wiring. Some measures have been taken to prevent this migration, and measures such as applying a moisture-proof paint to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied. It was not enough effect.

[0004] Further, in order to obtain a conductor having good conduction resistance, the amount of silver powder must be increased, and the silver paste is expensive, so that the conductive paste becomes expensive.
Using silver-coated copper powder can improve migration,
By using this, an inexpensive conductive paste can be obtained. However, if the silver coating is uniformly and thickly coated, there is no effect of improving migration. In addition, there is a disadvantage that soldering cannot be directly applied to the obtained conductive paste coating film. In addition, when soldering is performed on a conductive paste using silver powder, there is a disadvantage that silver is eroded and bonding cannot be sufficiently performed.

On the other hand, in a conductive paste using copper powder, since the copper is highly oxidizable after heat curing, oxygen contained in the air and in the binder reacts with the copper powder to form an oxide film on the surface thereof. And significantly lowers the conductivity. For this reason, various additives have been added to prevent copper powder from being oxidized, and a copper paste having a stable conductivity has been disclosed. However, the conductivity is not as high as that of the silver paste, and the storage stability has disadvantages. there were.
In addition, the conventional copper paste cannot directly apply soldering to the obtained copper paste coating film.

Conventionally known conductive pastes cannot be directly applied by soldering as described above. Therefore, a coating of the conductive paste is subjected to an activation treatment and subjected to electroless plating, or an electrolytic copper is used as a cathode as a coating. After plating, soldering was performed on the copper surface. However, it is not practical unless the bonding between the coating and the copper plating is ensured. Therefore, if a solderable conductive paste that does not need to be subjected to electroless plating or electroplating is developed, the circuit forming process is greatly shortened, and the merit thereof is great.

[0007] Solder is easy to bond with metal, but not with binder. In the case of soldering, ideally, a coating film of only the conductive powder may be formed and soldering may be performed thereon. However, using only the conductive powder causes problems in reliability and workability in forming the coating film. Therefore, a binder is used and a conductive paste is used. However, in order to emphasize the reliability and the workability of forming the coating film, if the ratio of the binder is increased, the binder covers the conductive powder which is a metal, and the area where the solder and the conductive powder come into contact with each other is lost. No longer adhere, and the conductivity also decreases.

On the contrary, when the soldering property is emphasized and the ratio of the conductive powder is increased, the viscosity of the conductive paste becomes extremely high, making the preparation of the conductive paste difficult, and the workability of applying the conductive paste is also increased. become worse. Also, the strength of the coating film is reduced because the amount of binder for binding the conductive powders is small. Therefore, when soldering is performed using a conductive paste, a conductive paste that balances solderability, conductivity, workability, and strength is required.

[0009]

SUMMARY OF THE INVENTION The first aspect of the present invention provides a conductive paste having excellent solderability. The second, third, fourth, and fifth aspects of the present invention provide a conductive paste having an excellent effect of improving solderability.

[0010]

The present invention comprises a conductive powder and a binder, and the compounding ratio of the conductive powder and the binder is 45:55 to 45:55 by volume ratio to the solid content of the conductive paste. The conductive powder: binder is 88:12 to 96.5: 3.5 at a weight ratio of 79:21 and the glass transition point (Tg) of the cured conductive paste is 40 to 180 ° C.
A conductive paste. Further, the present invention, the binder is mainly composed of an epoxy resin composition and its curing agent,
The epoxy equivalent of the epoxy resin is 160 to 330 g / eq.
A conductive paste.

Further, the present invention provides an epoxy resin composition comprising:
It contains a liquid epoxy resin at room temperature and a flexibility-imparting agent, and the mixing ratio of the epoxy resin and the flexibility-imparting agent is 40:60 to 90:10 by weight ratio.
A conductive paste. The present invention also relates to a conductive paste in which the conductive powder exposes a part of the copper powder or the copper alloy powder, and has a surface substantially covered with silver, and a substantially spherical shape. Furthermore, in the present invention, the conductive powder has a specific surface area of 0.1 to
It is a copper powder or a copper alloy powder having an average particle diameter of 1 to 20 μm having an aspect ratio of 1 to 1.5 and a major axis of 1.0 m ² / g, and the exposed area of the copper powder or the copper alloy powder is 10 to 60%. And a conductive paste which is a substantially spherical conductive powder.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in order to directly solder a conductive paste to a coating film, the mixing ratio of the conductive powder and the binder is determined by volume ratio with respect to the solid content of the conductive paste. Is in the range of 45:55 to 79:21, preferably in the range of 50:50 to 72:28,
The weight ratio is in the range of 88:12 to 96.5: 3.5 with the conductive powder: binder relative to the solid content of the conductive paste.
The ratio is preferably in the range of 90:10 to 95: 5. When the conductive powder falls below the above range, the solderability decreases. When the conductive powder exceeds the above range, the viscosity of the conductive paste becomes extremely high. And the workability of applying the conductive paste is deteriorated.

In the present invention, the glass transition point (hereinafter referred to as Tg) of the cured conductive paste is 40 to 180.
° C, preferably in the range of 40-140 ° C,
When the temperature is out of the range of 80 ° C., it becomes impossible to directly solder the coating film of the conductive paste.

The Tg of the cured conductive paste is 40 to 180.
In order to control the temperature in the range of ° C, it is preferable to use an epoxy resin composition and a curing agent thereof as a main component as a binder and an epoxy resin having an epoxy equivalent in the range of 160 to 330 g / eq. It is more preferable to use those in the range.

As the above-mentioned epoxy resin composition, it is preferable to use one containing a flexibility-imparting agent in addition to the epoxy resin. The mixing ratio of the epoxy resin and the flexibility imparting agent is
Epoxy resin: flexibility imparting agent in a weight ratio of 40:60 to 9
A range of 0:10 is preferred, and 50:50 to 8
Those having a ratio of 0:20 are more preferred.

The epoxy resin in the present invention is preferably liquid at room temperature. Those that crystallize at room temperature can avoid crystallization by mixing with a liquid. The epoxy resin that is liquid at room temperature in the present invention includes, for example, a resin that is solid at room temperature and becomes liquid at room temperature by mixing with an epoxy resin that is liquid at room temperature. In the present invention, the normal temperature means a temperature of about 25 ° C.

As the epoxy resin used in the present invention, a known epoxy resin is used. Compounds containing two or more epoxy groups in the molecular weight, for example, bisphenol A, bisphenol AD, bisphenol F, novolak, cresol novolaks and epichlorohydrin are used. Polyglycidyl ether obtained by the reaction, dihydroxynaphthalenediglycidyl ether, butanediol diglycidyl ether, heterocyclic epoxy such as diglycidyl hydantoin and aliphatic epoxy resin such as neopentyl glycol diglycidyl ether, vinyl cyclohexene dioxide,
Alicyclic epoxy resins such as dicyclopentanedienedoxide and alicyclic diepoxy adipate are exemplified.

As the flexibility-imparting agent, known ones are used, and compounds having only one epoxy group in the molecular weight, for example, n
Ordinary epoxy resins such as -butyl glycidyl ether, glycidyl versatate, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether, butylphenyl glycidyl ether and the like can be mentioned. These epoxy resins and flexibility-imparting agents can be used alone or in combination of two or more.

Examples of the curing agent added to the binder include amines such as mensendiamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, methylenedianiline, phthalic anhydride, trimellitic anhydride, and the like. Acid anhydrides such as pyromellitic anhydride, succinic anhydride, and tetrahydrophthalic anhydride, compound-based curing agents such as imidazole and dicyandiamide, and resin-based curing agents such as polyamide resins, phenol resins, and urea resins are used. Accordingly, it may be used in combination with a curing agent such as a latent amine curing agent, and generally, a tertiary amine, imidazoles, triphenyl phosphine, tetraphenyl phosphenyl borate, etc. are generally used in combination with an epoxy resin and a phenolic curing agent. Known as a curing accelerator The compound may be added.

The content of these curing agents is preferably in the range of 0.1 to 25 parts by weight with respect to 100 parts by weight of the epoxy resin in terms of Tg of the cured conductive paste.
More preferably, it is in the range of 20 parts by weight.

To the binder used in the present invention, in addition to the above-mentioned materials, if necessary, a thixotropic agent, a coupling agent, an antifoaming agent, a powder surface treating agent, an anti-settling agent, and a solvent are added and uniformly mixed. Is obtained. The thixotropic agent, coupling agent, defoaming agent, powder surface treating agent, anti-settling agent and the like added as necessary may be known ones, and the content thereof is 0.01 to 1 weight with respect to the conductive paste. %, More preferably 0.03 to 0.5% by weight.

The solvent to be added as required may be a known solvent, and its content is preferably in the range of 0.01 to 15% by weight with respect to the conductive paste.
More preferably, it is in the range of 10 to 10% by weight.

As the conductive powder, it is preferable to use a silver-coated copper powder or a silver-coated copper alloy powder whose surface is substantially covered with silver by exposing a part of the copper powder or the copper alloy powder. Is preferred from the viewpoint of preventing oxidation. If the entire surface is coated with silver without exposing a part of the copper powder or the copper alloy powder, the solderability is deteriorated and the object of the present invention tends to be unable to be achieved, and the migration property is deteriorated. Tend to.

As the copper powder or copper alloy powder, powder produced by an atomizing method is preferably used, and the smaller the particle size is, the more preferable it is. For example, a powder having an average particle size in the range of 1 to 20 μm is preferable. Powders in the range from 10 to 10 μm are more preferred. The exposed area of the copper alloy powder is preferably in the range of 10 to 60%, more preferably in the range of 10 to 50%, and more preferably 10 to 30%, from the viewpoint of solderability, oxidation of the exposed portion, conductivity and the like.
Is more preferable.

There are methods such as displacement plating, electroplating, and electroless plating for coating the surface of the copper powder or copper alloy powder with silver. Since the cost is low, it is preferable to cover with displacement plating. The amount of silver coating on the surface of the copper powder or copper alloy powder is 5 to 25% by weight based on the copper powder or copper alloy powder from the viewpoints of migration resistance, cost, and improvement in conductivity.
Is more preferable, and the range of 10 to 23% by weight is more preferable.

When the conductive powder has few contact points, the resistance tends to increase. In order to increase the contact area between the conductive particles and obtain high conductivity, it is preferable to apply a shock to the conductive powder to deform the shape of the particles into a flat shape, but the conductive paste using the flat conductive powder is substantially Viscosity is higher than conductive paste using spherical conductive powder. To reduce the viscosity, a large amount of a solvent may be contained. However, if a large amount of the solvent is contained, the thickness of the cured coating film is reduced by the volume of the solvent. In order to make the surface of the coating film flat and free from irregularities, polishing may be performed, but polishing is not preferred because the film thickness is reduced. Therefore, it is preferable to use a conductive paste using substantially spherical conductive powder from the viewpoint of workability and conductivity of the conductive paste.

The substantially spherical conductive powder in the present invention has a specific surface area of 0.1 to 1.0 m ² / g and an aspect ratio of 1 to 1.
It is preferable to use a conductive powder having an average particle diameter of 1.5 and a major axis of 1 to 20 μm, and a specific surface area of 0.1 to 0.6.
It is more preferable to use conductive powder having m ² / g, an aspect ratio of 1 to 1.3, and a long diameter having an average particle diameter of 1 to 10 μm because the effect of improving solderability is excellent. The specific surface area can be measured by a BET method, and the average particle diameter can be measured by a laser scattering type particle size distribution analyzer. In the present invention, the measurement was performed using a master sizer (manufactured by Malvern) as the device.

The aspect ratio in the present invention refers to the ratio of the major axis to the minor axis (major axis / minor axis) of the conductive powder particles. In the present invention, the particles of the conductive powder are mixed well in a curable resin having a low viscosity, and the resin is cured as it is by allowing the particles to settle by standing, and the resulting cured product is cut in the vertical direction. The shape of the particles appearing on the cut surface is observed under magnification with an electron microscope, and the major axis / minor axis of each particle is obtained for at least 100 particles, and the average value thereof is defined as the aspect ratio.

Here, the minor axis is selected so that a particle appearing on the cut surface is sandwiched by a combination of two parallel lines that are in contact with the outside of the particle. This is the distance between the parallel lines. On the other hand, the major axis is the two parallel lines perpendicular to the parallel line that determines the minor axis, and is the distance between the two parallel lines that are the longest among the combinations of the two parallel lines that contact the outside of the particle. is there. The rectangle formed by these four lines is sized to fit the particle exactly inside it. The specific method used in the present invention will be described later.

The conductive paste of the present invention is used together with the binder, the conductive powder and, if necessary, a thixotropic agent, a coupling agent, a defoaming agent, a powder surface treating agent, an anti-settling agent, etc. It can be obtained by uniformly mixing and dispersing with a kneader, three rolls or the like.

[0031]

The present invention will be described below with reference to examples. Example 1 60 parts by weight of epoxy resin (trade name: 140C, epoxy equivalent: 195 to 215 g / eq, manufactured by Mitsui Chemicals, Inc.), 40 weight parts of aliphatic diglycidyl ether (trade name: ED-503, manufactured by Asahi Denka Kogyo KK) 3 parts by weight of 2-phenyl-4-methyl-imidazole (manufactured by Shikoku Chemicals Co., Ltd., trade name: Curesol 2P4MHZ) and 3 parts by weight of dicyandiamide were uniformly mixed to form a binder.

Next, spherical copper powder having an average particle size of 5.1 μm produced by an atomizing method (manufactured by Nippon Atomize Processing Co., Ltd.
After washing (trade name: SFR-Cu) with dilute hydrochloric acid and pure water,
80 g of AgCN and 75 g of NaCN per liter of water
Was subjected to displacement plating so that the amount of silver was 18% by weight with respect to the spherical copper powder, washed with water and dried to obtain silver-plated copper powder.

Thereafter, 750 g of the silver-plated copper powder obtained above and 3 kg of zirconia balls having a diameter of 5 mm were put into a 2 liter ball mill container, and rotated for 40 minutes to give a specific surface area of 0.16 m ² / g. 1.3 average aspect ratio
In addition, a substantially spherical silver-plated copper powder having an average major diameter of 5.5 μm was obtained. Five particles of the obtained substantially spherical silver-plated copper powder were taken out and quantitatively analyzed by a scanning Auger electron spectrometer to examine the exposed area of copper. The average was 20% in the range of 10 to 50%. .

Ethyl carbitol 11 was added as a solvent to 35 g of the binder obtained above and 465 g of the substantially spherical silver-plated copper powder.
g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

The obtained conductive paste was heat-treated at 170 ° C. for 90 minutes to obtain a cured conductive paste, and the Tg of the cured conductive paste was converted to TMA1 manufactured by Seiko Denshi Kogyo.
As a result of measurement under the conditions of a load of 3 g and a heating rate of 5 ° C./min at 20, the result was 68 ° C.

The ratio of the conductive powder to the binder was 63:37 by volume, and 93: 7 by weight, and the ratio of the epoxy resin to the flexibility-imparting agent was by weight: The flexibility-imparting agent was 60:40.

Next, the copper foil of a 1.0 mm thick paper phenol copper-clad laminate (trade name: MCL-437F, manufactured by Hitachi Chemical Co., Ltd.) was removed from the conductive paste obtained above by etching. On the surface as shown in FIG.
Heat treatment was performed at 0 ° C. for 90 minutes to obtain a conductor 2. FIG. 1
1 is a paper phenol copper-clad laminate.

The surface of the obtained conductor 2 is polished with a water-resistant abrasive paper of # 3000 to make the surface of the conductor 2 smooth and mirror-finished, and then a solder flux is applied to the smooth and mirror-finished surface, and then a solder bath is formed. Immersion. Thereafter, the conductor was lifted from the solder bath, left to cool to room temperature, and cooled, and then a tape test (a test in which an adhesive tape was applied and then peeled off) was performed on the soldered portion of the surface of the conductor 2. As a result, it was confirmed that the solder did not adhere to the tape and was soldered to the surface of the conductor 2.

The specific method of measuring the aspect ratio in this embodiment will be described below. 8 g of a base material (No. 10-8130) of a low-viscosity epoxy resin (manufactured by Buehler Co.) and 2 g of a curing agent (No. 10-8132) are mixed, and 2 g of conductive powder is mixed and dispersed well, and the mixture is left as it is. After degassing in vacuo at a temperature of 10 ° C., the particles were allowed to stand at 30 ° C. for 10 hours to settle and harden the particles. Thereafter, the obtained cured product was cut in the vertical direction, the cut surface was magnified 1000 times with an electron microscope, and the long diameter / short diameter of 150 particles that appeared on the cut surface was obtained. Ratio.

Example 2 50 parts by weight of the epoxy resin used in Example 1, 50 parts by weight of the aliphatic diglycidyl ether used in Example 1, and 2-phenyl-4-methyl-imidazole 2 used in Example 1
Parts by weight and 3 parts by weight of dicyandiamide were uniformly mixed to prepare a binder.

Next, 475 g of the roughly spherical silver-plated copper powder obtained in Example 1 and 11 g of ethyl carbitol as a solvent were added to 25 g of the binder obtained above, and the mixture was uniformly mixed with a stirrer and a triple roll. The conductive paste was obtained by dispersion.

The obtained conductive paste was heat-treated at 170 ° C. for 90 minutes to obtain a cured conductive paste, and the Tg of the cured conductive paste was measured in the same manner as in Example 1. Was.

The ratio of the conductive powder to the binder was 71:29 by volume, and 95: 5 by weight, and the ratio of epoxy resin to the flexibility-imparting agent was epoxy resin: weight by weight. The flexibility-imparting agent was 50:50.

Next, a conductor was produced through the same steps as in Example 1, and a tape test was performed in the same manner as in Example 1. As a result, no solder was attached to the tape, and the tape was soldered to the conductor. Was confirmed.

Comparative Example 1 485 g of the roughly spherical silver-plated copper powder obtained in Example 1 and 11 g of ethyl carbitol as a solvent were added to 15 g of the binder obtained in Example 1, and the mixture was uniformly mixed with a stirrer and a three-roll mill. Although mixed and dispersed, it was a conductive paste having a high viscosity and was difficult to apply. For this reason, the tape test for producing the conductor was not performed.

The ratio of the conductive powder to the binder was 81:19 by volume, and 97: 3 by weight, and the ratio of the epoxy resin and the flexibility-imparting agent was by weight: The flexibility-imparting agent was 60:40.

Comparative Example 2 To 75 g of the binder obtained in Example 1 was added 425 g of the substantially spherical silver-plated copper powder obtained in Example 1 and 11 g of ethyl carbitol as a solvent, and the mixture was uniformly mixed with a stirring mill and a three-roll mill. After mixing and dispersion, a conductive paste was obtained.

The obtained conductive paste was heat-treated at 170 ° C. for 90 minutes to obtain a cured conductive paste, and the Tg of the cured conductive paste was measured in the same manner as in Example 1. Was.

The ratio of the conductive powder to the binder was 42:58 by volume and 85:15 by weight.
The ratio between the epoxy resin and the flexibility-imparting agent was 60:40 in weight ratio of epoxy resin: flexibility-imparting agent.

Next, a conductor was manufactured through the same steps as in Example 1, and a tape test was performed in the same manner as in Example 1. As a result, solder was adhered to the tape and could not be soldered to the conductor. .

Comparative Example 3 100 parts by weight of the epoxy resin used in Example 1 and a phenol resin (manufactured by Kanebo Co., Ltd., trade name: Bellpearl S-895)
16 parts by weight, 6 parts by weight of 2-phenyl-4-methyl-imidazole and 4 parts by weight of dicyandiamide used in Example 1 were uniformly mixed to prepare a binder.

Next, 465 g of the substantially spherical silver-plated copper powder obtained in Example 1 and 11 g of ethyl carbitol as a solvent were added to 35 g of the binder obtained above, and the mixture was uniformly mixed with a stirrer and a three-roll mill. The conductive paste was obtained by dispersion.

The obtained conductive paste was heated at 170 ° C. for 90 minutes to obtain a cured conductive paste, and the Tg of the cured conductive paste was measured in the same manner as in Example 1. As a result, the Tg was 186 ° C. Was.

The ratio of the conductive powder to the binder was 62:38 by volume, and 93: 7 by weight, and the ratio of the epoxy resin to the flexibility-imparting agent was by weight: The flexibility-imparting agent was 100: 0

Next, a conductor was produced through the same steps as in Example 1, and a tape test was conducted in the same manner as in Example 1. As a result, the solder adhered to the tape and could not be soldered to the conductor. .

Comparative Example 4 35 parts by weight of the epoxy resin used in Example 1, 65 parts by weight of the aliphatic diglycidyl ether used in Example 1, and 2-phenyl-4-methyl-imidazole 2 used in Example 1
Parts by weight and 2 parts by weight of dicyandiamide were uniformly mixed to prepare a binder.

Next, 465 g of the substantially spherical silver-plated copper powder obtained in Example 1 and 11 g of ethyl carbitol as a solvent were added to 35 g of the binder obtained above, and the mixture was uniformly mixed with a stirrer and a three-roll mill. The conductive paste was obtained by dispersion.

The obtained conductive paste was heat-treated at 170 ° C. for 90 minutes to obtain a cured conductive paste, and the Tg of the cured conductive paste was measured in the same manner as in Example 1. Was.

The ratio of the conductive powder to the binder was 61:39 by volume, and 93: 7 by weight, and the ratio of epoxy resin to the flexibility-imparting agent was by weight: The flexibility imparting agent was 35:65

Next, a conductor was produced through the same steps as in Example 1. Then, the surface of the conductor was polished with # 3000 water-resistant abrasive paper. The surface was distorted at the stage of making the surface smooth and mirror-finished, and the tape test could not be performed.

[0061]

The conductive paste according to claim 1 is excellent in solderability, and the conductive paste according to claims 2, 3, 4 and 5 is excellent in the effect of improving solderability.

[Brief description of the drawings]

FIG. 1 is a plan view of a conductor formed on a paper phenol copper-clad laminate.

[Explanation of symbols]

 1 Paper phenol copper clad laminate 2 Conductor

Claims (5)

[Claims] 1. A conductive powder and a binder, wherein the mixing ratio of the conductive powder and the binder is 45:55 to 79:21 in a volume ratio with respect to the solid content of the conductive paste, and the weight ratio is: Conductive powder: Binder 88: 12-96.5:
A conductive paste having a glass transition point (Tg) of 40 to 180 ° C. which is 3.5 and a cured conductive paste. 2. A binder comprising an epoxy resin composition and a curing agent thereof as a main component and an epoxy resin having an epoxy equivalent of 16
The conductive paste according to claim 1, wherein the amount is 0 to 330 g / eq. 3. The epoxy resin composition contains an epoxy resin which is liquid at room temperature and a flexibility-imparting agent, and the mixing ratio of the epoxy resin and the flexibility-imparting agent is epoxy resin: flexibility-imparting by weight ratio. The conductive paste according to claim 1 or 2, wherein the agent is 40:60 to 90:10. 4. The conductive paste according to claim 1, wherein the conductive powder exposes a part of the copper powder or the copper alloy powder and has a surface substantially covered with silver, and has a substantially spherical shape. 5. The conductive powder has a specific surface area of 0.1 to 1.0 m ^2.
/ G, a copper powder or a copper alloy powder having an aspect ratio of 1 to 1.5 and a long diameter of 1 to 20 μm, and an exposed area of the copper powder or the copper alloy powder of approximately 60% to 60%. 5. The conductive paste according to claim 1, 2, 3 or 4, which is a powder.