TW201338893A - Silver powder - Google Patents

Abstract

The present invention provides a novel silver powder, capable of enhancing silver concentration of a silver paste and forming a homogeneous with sintering conductor lower resistance. In the silver powder, D50 (referred to ''SEMD50'') obtained from image analysis of scanning type electron microscope (SEM) is 2.50 μ m to 7.50 μ m, a relationship of D10 (referred to ''SEMD10''), D50 (referred to ''SEMD50''), and D90 (referred to ''SEMD90'') obtained from image analysis of scanning type electron microscope (SEM) is shown in the relation formula: (SEMD90-SEMD10)/SEMD50 ≤ 0.50.

Description

Silver powder

The present invention relates to a silver powder which can be applied to a sintered conductive paste.

The conductive paste is a fluid composition in which a conductive filler is dispersed in a vehicle composed of a resin-based adhesive and a solvent, and is widely used for formation of an electric circuit or formation of an external electrode of a ceramic capacitor. Such a conductive paste has a resin-cured type in which a conductive paste is pressed by a resin to ensure conduction, and a sintered type in which an organic component is volatilized by high-temperature sintering and a conductive filler is sintered to ensure conduction.

The sintered conductive paste is generally a paste composition in which an electrically conductive filler (metal powder) and a glass frit are dispersed in an organic medium, and is volatilized at 400 to 800 ° C to volatilize the organic medium, and the sintered conductive filler is recombined. And ensure continuity. At this time, the glass frit has a function of attaching the conductive film to the substrate, and the organic medium acts as an organic liquid medium which can print the metal powder and the glass frit.

The silver powder used in the sintered conductive paste is conventionally required to be a fine particle of a specific electrode or a circuit, and is generally required to be fine particles and has a silver particle having a concentrated particle size distribution. Therefore, a corresponding novel technique has been proposed.

In addition, the silver powder has a dry silver powder prepared by a dry method and a wet silver powder produced by a wet method, but the wet silver powder is a single particle formed by a small crystallite collection, so that the firing temperature is lower than that of the dry silver powder. Characteristics.

Here, in the case of the wet silver powder, for example, Patent Document 1 proposes a fine particle silver powder which is obtained by image analysis of a scanning electron microscope image by monodispersion in which agglomeration of particles is small and has close dispersibility. the average particle diameter of D _IA is 0.6μm or less, the use of the primary particles of an average particle diameter D _IA and scattering particle size distribution determined by the method represented by the average particle diameter D ₅₀ to D ₅₀ by laser diffraction / D _IA The degree of agglomeration is 1.5 or less, the crystallite diameter is 10 nm or less, and the organic impurity content is 0.25 wt% or less in terms of carbon amount.

Further, Patent Document 2 proposes a spherical silver powder having an average particle diameter of 0.1 μm or more and less than 1 μm, a fine particle size distribution and high dispersibility, and a cumulative 10 mass% particle diameter measured by a laser diffraction method is represented as D10. The cumulative 50% by mass particle diameter is represented by D50, and the cumulative 90% by mass particle diameter is represented by D90. When the average particle diameter of the primary particles obtained by image analysis of the scanning electron microscope image is DSEM, the D50 is 0.1 μm or more. It is less than 1 μm, and the value of D50/DSEM is 1.3 or less, and the value of (D90-D10)/D50 is 0.8 or less.

(prior technical literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-48237

Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-70793

When a sintered conductor such as an electrode or a circuit is formed using a conductive paste, it is one of the important subjects to form a sintered conductor which is homogeneous and has a lower electric resistance, and a means for increasing the concentration of silver in the silver paste can be considered.

Here, the present invention provides novel silver powder which can increase the concentration of silver in the silver paste and form a sintered conductor which is homogeneous and has a lower electrical resistance.

The present invention provides a silver powder having a D50 (referred to as " _SEM D50") obtained by image analysis of a scanning electron microscope image (SEM) of 2.50 μm to 7.50 μm, and image analysis by scanning electron microscope image (SEM). The relationship between the obtained D10 (referred to as " _SEM D10"), D50 (referred to as " _SEM D50"), and D90 (referred to as " _SEM D90") is expressed by the relationship: ( _SEM D90- _SEM D10) / _SEM D50 ≦ 0.50 .

The silver powder proposed by the invention can increase the concentration of silver in the silver paste and form a sintered conductor which is homogeneous and has lower electrical resistance.

In the past, since the silver powder particles contain a large amount of fine particles, the total specific surface area is large, and a large amount of resin is required for preparing the silver paste. Therefore, it is difficult to increase the concentration of silver in the paste, and as a result, the electric resistance of the sintered conductor is increased. On the other hand, since the silver powder proposed by the present invention has a large particle diameter and a uniform particle diameter, the silver concentration in the silver paste can be increased, and a sintered conductor having a homogeneous and lower electric resistance can be formed.

Next, the present invention will be described based on the embodiments, but the present invention is not limited to the embodiments described below.

<本银粉>

The silver powder (hereinafter referred to as "the present silver powder") of the present embodiment has a D50 (referred to as " _SEM D50") obtained by image analysis of a scanning electron microscope image (SEM) of 2.50 μm to 7.50 μm, and is a scanning electron. The relationship between D10 (called " _SEM D10"), D50 (called " _SEM D50"), and D90 (referred to as " _SEM D90") obtained by image analysis of a microscope image (SEM) is the relationship: ( _SEM D90- _SEM D10) / _SEM D50 ≦ 0.50.

The characteristics of the silver powder are described below.

(wet silver powder)

The present silver powder includes either a wet silver powder produced by a wet method or a silver powder produced by a dry method. Among them, wet silver powder is preferred.

The wet silver powder is characterized by the formation of a single particle from a small crystallite collection, and thus has a characteristic of a large shrinkage ratio at 500 ° C in the TMA measurement as compared with the silver powder produced by the dry method. If the present silver powder is a wet silver powder, the shrinkage at 500 ° C in the TMA measurement is 1.0 to 23.0%, preferably 3.0% or more or 23.0% or less, and preferably 5.0% or more or 23.0% or less.

At this time, the shrinkage ratio measured by the above TMA can be measured as follows.

0.2 g of silver powder (sample) was used, and a load of 493 kg was applied to form a cylindrical shape of φ 3.8 mm. IKO-INSTRUMENTS thermomechanical analyzer (TMA) (EXSTAR6000TMA/SS6200), The linear shrinkage (%) in the longitudinal direction of the molded body was measured at a temperature increase rate of 20 ° C /min in an air atmosphere while applying a load of 98 mN, and a heat shrinkage ratio (%) at 500 ° C was obtained.

Further, according to the wet method, particles having a true spherical shape or a slightly spherical shape and having a large particle diameter can be produced. Even in the dry method, spherical particles can be produced by a spray method or a PVD method. However, it is difficult to produce true spherical particles by a spray method, and it is difficult to produce particles having a size as specified in the present invention even in a PVD method.

(D50)

In the present silver powder, it is important that the D50 (referred to as " _SEM D50") obtained by image analysis of a scanning electron microscope (SEM) image is 2.50 μm to 7.50 μm.

When the _SEM D50 of the present silver powder is 2.50 μm or more, the amount of the resin at the time of paste preparation can be reduced, and as a result, the electric resistance of the formed sintered conductor can be lowered. Further, when the _SEM D50 is 7.50 μm or less, it can be produced relatively stably.

Therefore, from the related viewpoint, the _SEM D50 of the present silver powder is preferably 3.00 μm or more or 6.50 μm or less, more preferably 3.00 μm or more or 5.50 μm or less.

(Particle size distribution)

In the silver powder, the relationship between D10 (referred to as " _SEM D10"), D50 (referred to as " _SEM D50"), and D90 (referred to as " _SEM D90") obtained by image analysis of a scanning electron microscope (SEM) image is The relationship: ( _SEM D90- _SEM D10) / _SEM D50 ≦ 0.50, this is important.

Here, D10 represents the number-based cumulative degree in the particle size distribution obtained by image analysis of a scanning electron microscope (SEM) image. The particle diameter is 10%, D50 is the particle diameter of 50% of the number of bases, and D90 is the particle diameter of 90% of the number of bases.

When the value of ( _SEM D90- _SEM D10)/ _SEM D50 is 0.50 or less, a conductive paste having a uniform particle size distribution and uniformity can be formed, and it can be sintered in a short temperature in a certain temperature range. From this point of view, the value of ( _SEM D90- _SEM D10) / _SEM D50 is preferably 0.20 or more or 0.44 or less, more preferably 0.20 or more or 0.40 or less.

However, even if a small amount of fine particles or coarse particles have little effect on the effect, the particle size tends to be uniform. If the value of ( _SEM D90- _SEM D10) / _SEM D50 is 0.50 or less, fine particles or coarse particles may be contained.

In addition, the distribution of ( _SEM D90- _SEM D10) / _SEM D50 has a apex and a singular peak with smooth slopes on both sides, which is different from the distribution by grading.

<Method>

Next, a specific manufacturing method of the preferred method for producing the silver powder will be described by a wet method. However, it is not limited to the wet method as described above.

In order to manufacture large-size silver powder by the conventional wet-reduction method, it is necessary to slowly carry out a process of regenerating the particles to grow the particles. However, if agglomerates having a small particle size or a small particle diameter are mixed, it is difficult to obtain a concentrated particle size distribution. Further, a large particle diameter can be produced by a spray method, but the sintering temperature becomes high due to excessively stable particles, and it becomes a silver powder which is not suitable for use in a sintered conductive paste. In addition to this, a large particle size and a concentrated particle size distribution can be obtained by classification, but there is a problem of productivity.

Here, the present invention succeeds in obtaining a silver powder having a large particle diameter and a uniform particle diameter by increasing the dissolved oxygen of the reductant solution used in the reductive reaction, and reacting the silver raw material solution, the reductant solution, and other additives in a static state. . That is, if the dissolved oxygen in the reductant solution is less, the reductive reaction starts immediately and forms fine particles. However, if the dissolved oxygen is large, the dissolved oxygen is first reacted, so that the silver reaction can be obtained until the time of precipitation. Therefore, during this period, the liquid composition of the reductant solution becomes a homogeneous and quiet state, and as a result, the particle size of the reductive precipitation tends to be uniform, and a wet silver powder having a large particle diameter of the primary particles and a uniform particle diameter can be obtained.

Here, a specific example of the method for producing the present silver powder will be described.

First, a staggering agent is added to a silver aqueous solution such as silver nitrate, and stearic acid such as Na or K stearate is added as needed, and after stirring, a resolving agent solution having an increased dissolved oxygen amount is added, and then a dispersing agent is added as needed, followed by stirring. The reaction causes the silver particles to be precipitated in a predetermined manner, and then the silver powder is obtained by a step of filtration, washing, drying, and the like.

Here, the reductant solution is prepared by adding a reductant (a hydrazine) to pure water, and at this time, the reductive amount can be adjusted by adding a reductant (a hydrazine) to the silver aqueous solution in pure water. The amount of dissolved oxygen in the solution. That is, if a reductant (diammine) is added to pure water, the dissolved oxygen originally contained in the pure water will be consumed by the reductive action of the reductant (the hydrazine), and will become less as time passes, so After the pure water is added to the reductant (diammine), it is preferably added to the silver solution as soon as possible in a short time.

However, it is also possible to ventilate pure water to increase the amount of dissolved oxygen in the solution.

In the above production method, an aqueous solution or slurry containing any one of silver nitrate, a silver salt complex, and a silver intermediate can be used as the silver aqueous solution such as silver nitrate.

Further, examples of the neutralizing agent include ammonia water, an ammonium salt, a chelate compound and the like.

Examples of the reductant include ascorbic acid, sulfite, alkanolamine, hydrogen peroxide water, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, metal hydride, dimethylamine borane An aqueous solution of a hydrazine, a hydrazine compound, hydroquinone, pyrogallol, glucose, gallic acid, formalin, anhydrous sodium sulfite, rongalite, or the like.

The dispersing agent may, for example, be a fatty acid, a fatty acid salt, a surfactant, an organic metal, a chelating agent, a protective colloid or the like.

(shape processing)

The silver powder can be directly used, but the silver powder can also be used after being processed into a shape.

For example, a spherical particle powder (a powder containing 80% or more of spherical particles) may be subjected to mechanical shape processing, and a non-spherical particle powder such as a flake, a scaly or a flat plate may be used (: 80% or more of non-containing powder) The powder of spherical particles is processed.

More specifically, it is mechanically flattened (press-stretched or stretched) using a bead mill, a ball mill, an attritor, a vibrating mill, or the like, whereby the shape can be processed into a flaky particle powder (: a powder containing 80% or more of flaky particles). At this time, in order to prevent particles Since the particles are processed in an independent state while being agglomerated or bonded to each other, it is preferred to add an auxiliary agent such as a fatty acid such as stearic acid or a surfactant.

Thus, the silver powder thus processed by the shape can be used, and it can also be used in combination with the unprocessed elemental powder.

Since the silver powder tends to have a uniform particle size, it is possible to effectively select a medium suitable for the particle size, so that even if it is a flake powder, homogeneous flake powder particles can be obtained.

It can also be a mixed powder of spherical powder and flake powder.

<Use>

The silver powder is suitable for silver powder for conductive paste, especially silver powder for sintered conductive paste.

For example, the present silver powder may be mixed with a glass frit in an organic medium to prepare a sintered conductive paste.

In this case, the glass frit may be, for example, lead-boron-glass or lead-free glass such as zinc-boron.

Further, as the resin binder, for example, any resin binder can be used. For example, it is preferable to use a composition containing one or more selected from the group consisting of epoxy resin, polyester resin, enamel resin, urea resin, acrylic resin, and cellulose resin.

<Description of statement>

In the present specification, the expression "X to Y" (X, Y is any number) includes "X or above Y" and "preferably greater than X" or "preferably less than Y" unless otherwise specified. meaning.

In addition, the performance "X or above" (X is an arbitrary number) or "Y" The following "(Y is an arbitrary number)" also includes "preferably greater than X_ or "preferably less than Y".

Example

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

The silver powder obtained in the examples and the comparative examples was evaluated for each characteristic by the method shown below.

(1) _SEM D10, _SEM D50, _SEM D90

A scanning electron microscope (SEM) image of any three fields of view was taken at 1000 to 3000 times using a scanning electron microscope (SEM) (SEM30 manufactured by PHILIPS), and changed to a BMP file, and IP-made by ASAHI-ENGINEERING Co., Ltd. _SEM D10, _SEM D50, and _SEM D90 were measured without a manual correction.

(2) Dissolved oxygen

The dissolved oxygen concentration in the aqueous hydrazine solution was measured using a DO (dissolved oxygen) meter (OM-51) manufactured by HORIBA.

(3) Evaluation of homogeneity

While adding a small amount of terpineol containing 5% ethylcellulose (100 cp) in a small amount of 3.5 g of silver powder, the mixture was stirred and mixed, and the amount of resin added (Xg) was measured at the time when the resin was dissolved. The following formula is used to determine the silver concentration in the paste, and the value of 95% or more is judged to be high in homogeneity.

(silver concentration (%) in the paste) = {(silver powder 3.5g) / (silver powder 3.5g) + resin addition amount Xg)}×100

<Example 1>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Next, 6 mL of an aqueous solution of a 1%-concentration amine dispersant (average molecular weight 10000) was added to an aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 6.00 to 8.00 mg/L of 11.9 g/ 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying. The obtained silver powder particles are slightly spherical.

<Example 2>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Next, 10 mL of a 1% aqueous solution of an amine-based dispersant (average molecular weight 10,000) was added to the aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 6.00 to 8.00 mg/L of 11.9 g/ 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying. Silver obtained The powder particles are slightly spherical.

<Example 3>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Then, 1 L of a hydrazine aqueous solution having a dissolved oxygen concentration of 6.00 to 8.00 mg/L and a concentration of 2.9 g/L of a fatty acid salt aqueous solution of 35 mL (concentration of 1 mol of silver) was added to an aqueous solution of silver ammonia complex at 20 ° C. A mixed solution of approximately 1.76 × 10 ^-3 mol) was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying. The obtained silver powder particles are slightly spherical.

<Example 4>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex. Then, 1 L of a hydrazine aqueous solution having a dissolved oxygen concentration of 6.00 to 8.00 mg/L and a concentration of 5 g/L of a gelatin aqueous solution of 48 mL (adjusted to 1 mol of silver) was added to an aqueous solution of silver ammonia complex at 20 ° C. 1.29 g) of the mixed solution, the reaction was carried out without stirring to precipitate silver particles.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying. The obtained silver powder particles are slightly spherical.

<Comparative Example 1>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Next, 6 mL of an aqueous solution of an amine-based dispersant (average molecular weight 10000) of 1% concentration was added to an aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 1.00 g / 5.00 mg / L of 11.9 g / 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

<Comparative Example 2>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Next, 6 mL of a 1% strength aqueous solution of an amine dispersant (average molecular weight 10000) was added to an aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 12.0 to 2.00 mg/L of 11.9 g/ 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

<Comparative Example 3>

Dissolve 50 mL of silver nitrate solution with a silver concentration of 400 g/L In 1 L of pure water, a silver nitrate aqueous solution was prepared, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous silver ammonia complex solution.

Next, 10 mL of a 1% aqueous solution of an amine-based dispersant (average molecular weight 10,000) was added to the aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 1.00 g/5.00 mg/L of 11.9 g/ 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

<Comparative Example 4>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Next, 10 mL of an aqueous solution of a 1%-concentration amine dispersant (average molecular weight 10000) was added to an aqueous solution of silver ammonia complex at 20 to 30 ° C and stirred, and the mixed dissolved oxygen concentration was adjusted to a concentration of 0.20 to 2.00 mg/L of 11.9 g/ 1 L of the aqueous hydrazine solution of L was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

<Comparative Example 5>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous solution of silver ammonia complex.

Then, 1 L of a hydrazine aqueous solution having a dissolved oxygen concentration of 0.20 to 2.00 mg/L and a concentration of 2.9 g/L of a fatty acid salt solution of 35 mL (1 mol of silver) was added to an aqueous solution of silver ammonia complex at 20 ° C. A mixed solution of approximately 1.76 × 10 ^-3 mol) was used to precipitate the silver particles without stirring.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

<Comparative Example 6>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 50 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous silver ammonia complex solution. Then, 1 L of a hydrazine aqueous solution having a dissolved oxygen concentration of 0.20 to 2.00 mg/L and a concentration of 5 g/L of a gelatin aqueous solution of 48 mL (adjusted to 1 mol of silver) was added to an aqueous solution of silver ammonia complex at 20 ° C. 1.29 g) of the mixed solution, the reaction was carried out without stirring to precipitate silver particles.

Subsequently, the silver particles were filtered, washed with water until the conductivity of the filtrate was 40 μS/cm or less, and then silver powder (sample) was obtained by drying.

(examine)

The silver powder of the embodiment is larger than the silver powder of the comparative example and the silver powder of the prior art, and the particle diameter tends to be uniform. Therefore, if the silver paste is used for the purpose, the silver concentration can be increased, and a sintered conductor having a homogeneous and lower electrical resistance can be formed. .

From this point of view, it is considered that the _SEM D50 of the present silver powder is 2.50 μm to 7.50 μm, and ( _SEM D90- _SEM D10) / _SEM D50 ≦ 0.50.

Claims (4)

A silver powder obtained by image analysis of a scanning electron microscope image (SEM) has a D50 (referred to as " _SEM D50") of 2.50 μm to 7.50 μm, and a D10 obtained by image analysis of a scanning electron microscope image (SEM). The relationship between (referred to as " _SEM D10"), D50 (referred to as " _SEM D50"), and D90 (referred to as " _SEM D90") is expressed by the relationship: ( _SEM D90- _SEM D10) / _SEM D50 ≦ 0.50. The silver powder described in claim 1 is a wet silver powder. A silver powder is formed by subjecting a silver powder according to item 1 or 2 of the patent application to a shape processing. A sintered conductive paste comprising the silver powder according to any one of claims 1 to 3.