JP6324288B2 - Conductive paste and electromagnetic shielding member - Google Patents

Description

  The present invention relates to a conductive paste and an electromagnetic wave shielding member. In particular, the present invention relates to a conductive paste that is excellent in film formability and exhibits good shielding properties in a wide range of silver powder blending amounts, and an electromagnetic wave shielding member obtained by processing such a conductive paste into a film shape.

In recent years, with the rapid development of high-capacity and high-speed communication technology using small and lightweight mobile terminals, high-speed wireless transmission technology and multifunctional terminal devices are required to be small and thin.
Along with this, in the semiconductor mounting field, electronic components have been packed in a limited area by multilayer boards and narrow pitch mounting, but they are approaching the limit.
For this reason, for example, in an electronic circuit module component, a technique has been developed in which various active elements / passive elements that are surface-mounted on a circuit board are incorporated in a laminated board or three-dimensionalized.
Further, in an electronic circuit module, a sheet metal member is used as an electromagnetic wave shield on the outside of an insulating resin that is a sealing layer. By using the sheet metal member as a metal layer using a conductive paste, the electronic circuit module It becomes possible to make the outer diameter of a part smaller.

As such a conductive paste, for example, a conductive silver paste that is different in circuit formation to be miniaturized and can form a circuit having better conductivity than a conventional conductive silver paste, and such a conductive silver An electromagnetic shielding member using a paste has been proposed (see, for example, Patent Document 1).
More specifically, it is a conductive silver paste containing silver powder, a binder resin and a solvent, and the silver powder is a silver particle (A) having an average particle size of 0.5 μm to 20 μm, more preferably an average particle size. Is composed of scaly silver particles having a particle size of 2 μm to 10 μm and spherical silver particles (B) having an average primary particle size of 50 nm or less, and the mixing ratio (weight ratio) is (A) :( B) A conductive silver paste characterized by being in the range of 99: 1 to 80:20 is disclosed.

In addition, a heat-curable conductive paste composition has been proposed that has excellent printability, high conductivity, and good solder wettability (see, for example, Patent Document 2).
More specifically, it is a thermosetting conductive paste composition comprising (A) silver powder, (B) a thermosetting component, (C) a curing agent, and (D) a solvent, A) As silver powder, (a1) includes a flaky silver powder having an average particle diameter of 2 to 20 μm, and (a2) a spherical silver powder to which a surface treatment agent having an average particle diameter of 4 to 20 μm is attached, and The heat-curable conductive paste composition is characterized in that the ratio of (A) silver powder in the solid content is 90 to 95% by weight.

In addition, in a thin product such as an IC card that is stressed during use, there has been proposed a conductive paste that can withstand connection stress and provide connection reliability that prevents contact from being removed (for example, (See Patent Document 3).
More specifically, a module having (A) urethane acrylate, (B) acrylic monomer, (C) organic peroxide, (D) conductive powder, and (E) metal soap as essential components. A conductive paste for connection is disclosed.

JP-A-2005-294254 (Claims etc.) JP2011-71057 (Claims etc.) JP 2010-176894 (Claims etc.)

However, since the conductive silver paste disclosed in Patent Document 1 has a small primary particle diameter of the spherical silver particles (B) and an excessively low blending ratio with the scaly silver particles (A), the conductive silver paste has a predetermined conductivity. In order to obtain the properties, the total amount of silver particles (A + B) is increased to about 87% by weight or more (see Examples 1 to 4), so that the viscosity and specific gravity of the conductive silver paste are increased. There have been problems such as poor applicability, film formability, and economical disadvantage.
In addition, since the primary particle size of the spherical silver particles (B) is small and the blending ratio with respect to the flaky silver particles is excessively small, it is difficult to form a silver powder laminated structure described later, which is favorable. There was also a problem that shield characteristics could not be obtained.

In addition, in the heat-curable conductive paste composition disclosed in Patent Document 2, in order to obtain a predetermined conductivity, the total amount of silver particles (a1 + a2) needs to be 90% by weight or more. As a result, the viscosity and specific gravity of the conductive silver paste are increased, so that the coating property is lowered, the film forming property is lowered, and further, it is economically disadvantageous.
In addition, since the average particle size of the spherical silver powder to which (a2) the surface treatment agent is adhered is excessively large, it is difficult to form a silver powder laminated structure to be described later, and good shielding properties are obtained. There was also a problem that could not be obtained.

Furthermore, in the conductive paste for module connection disclosed in Patent Document 3, in order to obtain predetermined conductivity, (D) a configuration in which the blending amount of the conductive powder is increased to about 85% by weight (Example 1). Therefore, it is said that the viscosity and density of the conductive silver paste are increased, the coatability is lowered, the film formability is lowered, and further, it is economically disadvantageous. There was a problem.
Moreover, the urethane acrylate resin is used as the main component as the resin component, while the acrylic monomer contained as the curing component in the resin component is intended to be cured using an organic peroxide and a curing accelerator. For this reason, there was a problem that the conductive paste was not sufficiently cured, or the adhesive strength of the obtained conductive cured product to the electronic substrate (glass fiber reinforced epoxy substrate, etc.) was low.

Therefore, as a result of intensive studies, the present inventors have used (A) silver powder as a combination of (a1) a predetermined flaky silver powder and (a2) a predetermined non-flaky silver powder, and (B) a binder resin. (C) A silver powder laminate structure (sandwich) in which a non-flaky silver powder is contained in a gap in the vertical direction of a horizontally oriented flaky silver powder as well as easily forming a flexible conductive film by further containing a solvent. The present invention has been completed by finding that good shielding properties can be obtained regardless of the total amount of these silver powders.
That is, the present invention is a conductive paste that is excellent in film formability and exhibits good shielding characteristics in a wide range of silver powder blending amounts, and an electromagnetic wave shield obtained by processing such a conductive paste into a film shape. An object is to provide a member.

According to the present invention, a conductive layer is formed on an electronic substrate that includes (A) silver powder, (B) a binder resin, and (C) a solvent. When the (A) silver powder is a plan view of (a1), the average particle diameter as the equivalent circle diameter is a value in the range of 5 to 30 μm, and the thickness is 0. A flaky silver powder having a value in the range of 0.01 to 2 μm, and (a2) an average particle size in the range of 1 to 5 μm, and a bulk density in the range of 0.3 to ³ g / cm ³ Non-flaky silver powder that is a value, and (A) the total blending amount (a1 + a2) of silver powder is a value within the range of 40 to 240 parts by weight with respect to 100 parts by weight of (B) binder resin. When the conductive layer is formed, the upper and lower sides of a plurality of (a1) flaky silver powders are horizontally oriented. The gap, (a2) non-flaky silver powder, characterized in that to form a silver layered structure composed penetrates conductive paste is provided, it is possible to solve the problems described above.
That is, as (A) silver powder, (a1) a predetermined flaky silver powder and (a2) a predetermined non-flaky silver powder are used in combination, and (B) a binder resin and (C) a solvent are further included. In addition to obtaining a flexible conductive film, it is easy to form a silver powder laminate structure in which non-flaky silver powder enters in the vertical gap of horizontally oriented flaky silver powder. Good shielding characteristics can be exhibited.
In addition, about the formability of a silver-powder laminated structure, although judgment criteria are shown in Example 1, if it is formed even if the silver-powder laminated structure is a part (for example, about 10 to 30% of the total volume). It has been proved separately that it exhibits a certain shielding property.

Moreover, when composing the conductive paste of the present invention, it is preferable that the shape of (a1) flaky silver powder when viewed in plan is a circle or an ellipse.
By using flaky silver powder having such a planar shape, it is possible to form a conductive layer that is easy to bend from any direction, and further, in the gap in the vertical direction of horizontally oriented flaky silver powder, Since it becomes easier to form a silver powder laminated structure in which non-flaky silver powder enters, it is possible to exhibit even better shielding characteristics in a wide range of blending amounts of silver powder.

In constituting the conductive paste of the present invention, it is preferable that the (a2) non-flaky silver powder is either a chestnut-shaped silver powder or a spherical silver powder.
By using the non-flaky silver powder having such a three-dimensional shape, it becomes easy to stay in the gap in the vertical direction etc. of the horizontally oriented flake silver powder. Good shielding characteristics can be exhibited.

Moreover, in composing the conductive paste of the present invention, the blending ratio (weight ratio) of (a1) flaky silver powder and (a2) non-flaky silver powder is a value within the range of 80:20 to 40:60. It is preferable to do.
By such a blending ratio, the formability of the conductive film is further improved, the adhesion to the electronic substrate and the like, the follow-up to the three-dimensional unevenness on the surface of the electronic substrate, etc., and further It becomes easy to balance with good shielding characteristics.

In constituting the conductive paste of the present invention, it is preferable that (B) the binder resin be at least one of an epoxy resin, a polyester resin, and a urethane acrylic resin.
By using such a resin, the film formability can be further improved, and the adhesion to an electronic substrate and the followability to the three-dimensional unevenness on the surface of the electronic substrate can be further improved.

Further, in constituting the conductive paste of the present invention, (C) the solubility parameter (SP value) of the solvent is set to a value within the range of 8.0 to 11.0, and the boiling point is within the range of 70 to 180 ° C. It is preferable to set the value of.
By using such a solvent (C), the handleability of the conductive paste can be improved, and the film formability can be further improved.

Further, in configuring the conductive paste of the present invention, it is preferable to set the specific resistance of the cured product of the conductive paste (silver powder content: 60 wt%) to a value of 1 × 10 ⁻³ Ohm · cm or less.
By setting the specific resistance of the cured product of the conductive paste within a predetermined value range, the balance between adhesion to electronic substrates and the like, followability to three-dimensional irregularities on the surface of electronic substrates and the like, and good shielding properties are achieved. It is even easier to take.

Another aspect of the present invention is an electromagnetic wave shielding member characterized in that any of the conductive pastes described above is formed into a film.
By comprising in this way, while being able to acquire the favorable followable | trackability and adhesiveness to the three-dimensional unevenness | corrugation in the surfaces, such as an electronic substrate, a favorable shield characteristic can be exhibited.

FIGS. 1A to 1C are electron micrographs (each with a magnification of 500) of flaky silver powder (three types) having different average particle sizes and the like. FIG. 2 is an electron micrograph (magnification 1000) in a cross section of a conductive layer obtained by thermally curing a conductive paste. FIG. 3 is an electron micrograph (magnification 1000) in the plane of the conductive layer obtained by thermally curing the conductive paste. FIG. 4 is an electron micrograph (magnification 60) in a cross section of a partially conductive layer obtained by applying a conductive paste to an electronic substrate on which electronic elements are mounted and then thermally curing the paste. FIG. 5 is a particle size distribution chart of the flaky silver powder. FIG. 6 is a drawing provided to explain the relationship between the concentration (% by weight) of silver powder (two types) in a conductive paste and the specific resistance (Ohm · cm). FIG. 7 is a drawing provided to explain the relationship between the concentration (% by weight) of silver powder (two types) in the conductive paste and the shield characteristic (dB). FIG. 8 is a drawing provided to explain a shielded electronic substrate as an application example of the conductive paste to the electronic substrate on which the electronic element is mounted. FIG. 9 is a shield characteristic chart of the conductive paste (Example 1). FIG. 10 is a shield characteristic chart of the conductive paste (Comparative Example 1).

[First Embodiment]
The first embodiment includes (A) silver powder, (B) a binder resin, and (C) a solvent. A conductive layer is formed on an electronic substrate on which an electronic element is mounted, and a predetermined shield is formed. It is a conductive paste that exhibits the characteristics, and when (A) silver powder is (a1) in plan view, the average particle diameter as the equivalent circle diameter is a value within the range of 5 to 30 μm, and the thickness A flaky silver powder having a value in the range of 0.01 to 2 μm, and (a2) an average particle size in the range of 1 to 5 μm and a bulk density of 0.3 to ³ g / cm ³ It is a conductive paste containing non-flaky silver powder having a value within the range.
And (A) The compounding quantity of silver powder is set to the value within the range of 40-240 weight part with respect to 100 weight part of (B) binder resin, and when the conductive layer is formed, it is horizontally oriented. (A1) A conductive paste characterized in that (a2) a silver powder laminated structure in which non-flaky silver powder enters is formed in the vertical gap of the flaky silver powder.
Hereinafter, the conductive paste of the first embodiment will be specifically described with reference to the drawings as appropriate.

1. Basic Configuration The conductive paste according to the first embodiment includes (A) silver powder, (B) a binder resin, and (C) a solvent as basic components.
That is, with respect to 100 parts by weight of (B) binder resin, the amount of (A) silver powder is set to a value within the range of 40 to 240 parts by weight (about 25 to 70% by weight in terms of the total amount), and film formability This is to improve the balance with the shield characteristics and the like.
More specifically, when the blending amount of the silver powder (A) is less than 40 parts by weight, the film formability is improved, but the formation of a so-called sandwich structure is insufficient, and the shielding characteristics are reduced. It is because it falls remarkably.
On the other hand, when the blending amount of the silver powder (A) exceeds 240 parts by weight, the film formability and the surface followability with respect to the three-dimensional unevenness are remarkably lowered.
Therefore, it is more preferable to set the blending amount of (A) silver powder within a range of 80 to 200 parts by weight with respect to 100 parts by weight of (B) binder resin, and (A) the blending amount of silver powder is 100 to 200. More preferably, the value is within the range of parts by weight.
In addition, the conductive paste of the first embodiment preferably includes (D) a binder resin curing agent or a predetermined amount of the polymerization initiator when the binder resin includes a monomer component.
This is because (D) the binder resin is cured or the monomer component contained therein is polymerized to obtain a suitable adhesive force and good shielding properties.

2. (A) Silver powder (1) (a1) Flaky silver powder (A) As one of the silver powders, as shown in FIGS. In addition, flaky silver powder having an average particle diameter (D ₅₀ ) as an equivalent circle diameter in the range of 5 to 30 μm and a thickness in the range of 0.01 to 2 μm is used. And
The reason for this is that, by using such flaky silver powder, as shown in FIG. 2, non-flakes are formed in the gap in the vertical direction of the horizontally oriented flaky silver powder (partially, the gap between adjacent flaky silver powders). It is easy to form a silver powder laminated structure (sandwich structure) in which a silver powder enters, and when the amount of silver powder is relatively large (for example, 50% by weight or more of the total amount), This is because good shielding properties and film processability can be obtained even in a small amount (for example, less than 50% by weight of the total amount).
When the flaky silver powder and the non-flaky silver powder form a silver powder laminated structure, as shown in FIG. 3, the circular flaky silver powder is horizontally oriented and both surfaces of the flaky silver powder face upward or downward. Furthermore, since a part of the non-flaky silver powder also enters the gap between the horizontally oriented adjacent flaky silver powders, and not only the vertical direction but also the horizontal conduction is obtained, a relatively small amount of Even if it is the compounding quantity of silver powder, a favorable shield characteristic can be obtained.
In addition, the conductive layer comprising a flaky silver powder, a non-flaky silver powder, and a silver powder laminated structure formed from a predetermined resin is characterized by being extremely flexible.
Therefore, as shown in FIG. 4, even in the corner of an electronic element (semiconductor element) mounted on an electronic substrate, the shape of the corner follows the shape of the conductive layer while maintaining the silver powder multilayer structure. Since the flaky silver powder is easily deformed, good shielding properties can be exhibited.

More specifically, when the average particle diameter of the flaky silver powder as an equivalent circle diameter is less than 5 μm, the flaky silver powder in the horizontal direction is sparse because the particle diameter is excessively small, and sufficient silver powder lamination This is because the structure is not formed, and the shield characteristic may be deteriorated or the electric characteristic may be deteriorated.
On the other hand, if the average particle size of the flaky silver powder exceeds 30 μm, deformation during paste kneading becomes severe, and further, clogging may occur when applying to a coated object using a dispenser. It is because there is a case to do.
Therefore, the average particle size of the flaky silver powder is more preferably set to a value within the range of 7 to 25 μm, and further preferably set to a value within the range of 10 to 20 μm.
The average particle diameter (D ₅₀ ) of the flaky silver powder can be measured by a laser diffraction / scattering particle size distribution measuring device as an equivalent circle diameter in plan view, or measured from an electron micrograph. Further, it can be calculated from the electron micrograph using an image processing apparatus.

In addition, when the thickness of the flaky silver powder becomes a value of less than 0.01 μm, the mechanical strength may be lowered or it may be difficult to stably produce the flaky silver powder.
On the other hand, when the average thickness of the flaky silver powder exceeds 2 μm, it becomes difficult to deform, it becomes difficult to uniformly mix and disperse in the resin, or the manufacturing time becomes excessively long. Because there is.
Therefore, the average thickness of the flaky silver powder is more preferably set to a value in the range of 0.02 to 0.5 μm, and further preferably set to a value in the range of 0.05 to 0.2 μm.
The average thickness of the flaky silver powder can be measured from an electron micrograph as shown in FIGS. 1A to 1C, and further calculated from the electron micrograph using an image processing apparatus. You can also

Moreover, it is preferable to make the standard deviation of the particle size distribution in the predetermined average particle diameter (for example, 10 micrometers) of flaky silver powder into the value within the range of 1-5.
For example, FIG. 5 shows a particle size distribution chart of flaky silver powder (relationship between average particle diameter, measurement frequency, and cumulative frequency). From the particle size distribution chart, the standard deviation of the particle size distribution (2.3 in the example of FIG. 5) can be calculated from the following equation.
Standard deviation of particle size distribution = (d84% −d16%) / 2
d84%: particle diameter (μm) at which the cumulative frequency curve of particle size distribution is 84%
d16%: Particle diameter (μm) at which the cumulative frequency curve of particle size distribution is 16%
That is, when the standard deviation in the particle size distribution is less than 1, it follows the surface having a three-dimensional concavo-convex structure, the corner of the electronic element, etc. like an electronic board on which an electronic element (semiconductor element, etc.) is mounted. This is because it may be difficult to form a conductive layer having a uniform thickness, or the shielding properties of the conductive layer may be significantly reduced when the amount of silver powder is relatively small. .
On the other hand, when the standard deviation in the particle size distribution exceeds 5, particularly, the concentration distribution of the silver powder on the horizontal plane of the conductive layer becomes non-uniform, and the shield characteristics may be significantly deteriorated.
Therefore, it is more preferable to set the standard deviation of the particle size distribution in the predetermined average particle size (for example, 10 μm) of the flaky silver powder to a value in the range of 1.5 to 4, and to a value in the range of 2-3. Is more preferable.

Moreover, as an edge shape of flaky silver powder, it is preferable that it has a notch part along the said edge and has a jagged shape as a whole shape so that it may illustrate in FIG.1 (a)-(c).
The reason for this is that, in the form having such a cut-out portion at the peripheral edge, the flaky silver powder is more easily deformed, and when a conductive paste is formed, even better electrical characteristics can be obtained. is there.
That is, it can be easily deformed, the electrical contact between adjacent flaky silver powders becomes good, and further, the value of the bulk density described later can be effectively reduced.
Therefore, it is usually preferable to have a cutout portion having a depth of 0.01 to 3 μm, more preferably having a cutout portion having a depth of 0.05 to 2 μm along the edge of the flaky silver powder. It is more preferable to have a notch with a depth of 0.1 to 1 μm.
And it has become clear that it is suitable to make the compounding quantity of an organic acid into the value within the range of 0.001-1 weight% as manufacturing conditions about providing such a notch part.
In addition, along the edge of the flaky silver powder, whether or not it has a notch can also be observed from an electron micrograph, and further, from the electron micrograph, the degree of circularity can be determined using an image processing apparatus. It can be calculated and replaced.

Moreover, as illustrated in FIG. 1B, it is preferable to provide a plurality of minute protrusions on the surface (front surface and back surface) of the flaky silver powder.
The reason for this is that by providing a plurality of such microprojections on the surface, a plurality of flaky silver powders are arranged in the horizontal direction, and even if some of them overlap in the vertical direction, This is because the value of the bulk density can be further reduced because a space is easily formed between them.
On the other hand, since a plurality of flaky silver powders are arranged in a row in the horizontal direction, there is no change, so that not only in the horizontal direction but also in a vertical direction through a plurality of microprojections, it is good. This is because electrical conduction can be obtained.
Here, the height of the fine protrusion is not particularly limited, but is preferably set to a value in the range of 0.001 to 1 μm, for example, a value in the range of 0.005 to 0.5 μm. It is more preferable to set the value within the range of 0.01 to 0.2 μm.
And it has become clear that it is suitable to make the compounding quantity of an organic acid into the value within the range of 0.001-1 weight% as manufacturing conditions about providing such a microprotrusion part.
Note that the height of the minute protrusions on the surface of the flaky silver powder can be directly measured as an arithmetic average value using a surface roughness meter, or can be illuminated with a scale from an electron micrograph. It can be indirectly measured as an arithmetic average value.

Moreover, it is preferable to make the bulk density of flaky silver powder into the value within the range of 0.1-4 g / cm < ³ >.
The reason for this is that when the bulk density of the flaky silver powder is less than 0.1 g / cm ³ , dispersion in the resin becomes extremely difficult, the manufacturing process becomes complicated, and the manufacturing yield is significantly reduced. This is because there is a case of doing.
On the other hand, if the bulk density of the flaky silver powder exceeds 4 g / cm ³ , the shape retention of the flaky silver powder may be remarkably lowered or the conductivity may be lowered.
Therefore, preferably a value within the range of the flaky silver powder 0.5 to 3 g / cm ³ a bulk density of, more preferably to a value within the range of 0.7~3g / cm ^3, 1~ More preferably, the value is within the range of 2 g / cm ³ .
The bulk density of the flaky silver powder can be measured according to JIS K5101 tap method.

  The method for producing the flaky silver powder is not particularly limited. For example, based on the wet reduction method described below, a first aqueous solution containing silver nitrate and a second aqueous solution containing a silver nitrate reducing agent are provided. It is preferable that nitric acid and an organic acid are respectively blended in the first aqueous solution and the second aqueous solution, or any one of the aqueous solutions.

(First aqueous solution)
First, it is preferable to make the compounding quantity of silver nitrate in a 1st aqueous solution into the value within the range of 1 to 20 weight% normally.
The reason for this is that when the amount of silver nitrate is less than 1% by weight, the production rate of the flaky silver powder is excessively reduced, and the production efficiency may be significantly reduced.
On the other hand, if the blending amount of silver nitrate exceeds 20% by weight, the viscosity of the slurry deposited by reaction increases, which may make it difficult to control the reaction.
Therefore, the amount of silver nitrate contained in the first aqueous solution is more preferably set to a value within the range of 7 to 17% by weight, and further preferably set to a value within the range of 10 to 15% by weight.
Further, as will be described later, nitric acid can be blended only in the second aqueous solution, but when blending nitric acid as a form control agent in the first aqueous solution, the blending amount is based on the total amount of the first aqueous solution. Thus, the value is preferably 20% by weight or less.
That is, when the amount of nitric acid exceeds 20% by weight, a plurality of minute protrusions may grow abnormally as a surface state on the surface (front surface and back surface) of the flaky silver powder.
However, when the amount of silver nitrate is excessively reduced, the effect of addition may not be exhibited stably.
Therefore, it is more preferable to set the blending amount of nitric acid to a value in the range of 0.1 to 10% by weight, and a value in the range of 0.5 to 5% by weight with respect to the total amount of the first aqueous solution. More preferably.

As will be described later, the organic acid can also be blended in the second aqueous solution. However, when blending the organic acid as the form control agent in the first aqueous solution, the blending amount is adjusted to the total amount of the first aqueous solution. On the other hand, the value is preferably 2% by weight or less.
That is, when the blending amount of the organic acid exceeds 2% by weight, the shape of the silver powder is not flaky but may be almost spherical.
However, if the amount of the organic acid is excessively reduced, the effect of addition may not be exhibited stably.
Therefore, it is more preferable that the blending amount of the organic acid is a value within the range of 0.001 to 0.5% by weight with respect to the total amount of the first aqueous solution. More preferably, the value is within the range.
In addition, as an organic acid as such a form control agent, citric acid (including citric acid monohydrate), succinic acid, malic acid (including D-malic acid and L-malic acid), tartaric acid (mono tartaric acid) Hydrate, etc.), malonic acid, glutaric acid, adipic acid, formic acid, acetic acid, propionic acid, butyric acid and the like alone or in combination of two or more.

In addition, ammonia and / or an amine compound (hereinafter sometimes simply referred to as ammonia or the like) can be blended in the second aqueous solution as described later, but is blended in the first aqueous solution as a form control agent. When it does, it is preferable to make the compounding quantity into the value of 2 weight% or less with respect to the whole quantity of 1st aqueous solution.
That is, if the amount of ammonia or the like exceeds 2% by weight, the particle size of the obtained flaky silver powder may be too small.
However, when the amount of ammonia or the like is excessively small, the mixing effect cannot be obtained, and it may be difficult to control the average particle size.
Therefore, it is more preferable to set the blending amount of ammonia or the like to a value within the range of 0.1 to 1.5% by weight with respect to the total amount of the first aqueous solution, and within the range of 0.5 to 1% by weight. More preferably, it is a value.
In addition, ammonia etc. can be mix | blended as ammonia water (concentration 28%), for example, In that case, a compounding quantity will be determined in consideration of a density | concentration.

  Furthermore, preferred examples of the amine compound include diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylmonoethanolamine, N-ethylmonoethanolamine, N-butylmonoethanolamine, N- Methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-cyclohexyldiethanolamine, N, N-dimethylmonoethanolamine, N, N-diethylmonoethanolamidiethylmonoethanolamine, N, N-dibutylmonoethanolamine, amino Examples include alcohol amine compounds such as methyl propanol, aminoethyl propane diol, aminomethyl propane diol, and amino butanol.

  Also, the amount of water (ion exchange water) is the remaining amount of silver nitrate, nitric acid, aqueous ammonia, etc., and water is added so that the total amount of the first aqueous solution composed of these components is 100% by weight. To do.

Therefore, as a blending example of the first aqueous solution, silver nitrate, nitric acid, ammonia water, etc., and water are blended, respectively, and the blend of silver nitrate with respect to the total amount (100 wt%) of the first aqueous solution. The amount is a value within the range of 1 to 20% by weight, the amount of nitric acid is 20% by weight or less, the amount of ammonia water or the like is within the range of 2% by weight, and the amount of residual water is the amount of water. It is preferable.
As another blending example of the first aqueous solution, silver nitrate, nitric acid, ammonia water, etc., an organic acid, and water are blended, respectively, and the total amount (100% by weight) of the first aqueous solution is blended. On the other hand, the amount of silver nitrate is within a range of 1 to 20% by weight, the amount of nitric acid is 20% by weight or less, the amount of ammonia water or the like is 2% by weight or less, and the amount of organic acid is 2% by weight. It is preferable to set it as the amount of the remaining amount of water below.
Note that nitric acid, aqueous ammonia, and the like, and organic acid can be blended in the second aqueous solution, as described later. In that case, the blending amount of nitric acid, aqueous ammonia, and the organic acid in the first aqueous solution, It can be changed as appropriate.
More specifically, when nitric acid is blended in the first aqueous solution and the second aqueous solution, the total amount of nitric acid is set to a value within the range of 0.1 to 10% by weight with respect to the total amount thereof. Is preferred.
Similarly, when ammonia water or the like and an organic acid are blended in the first aqueous solution and the second aqueous solution, respectively, the total amount of ammonia water or the like and the organic acid with respect to the total amount of each, A value within the range of 0.001 to 1% by weight is preferred.

(Second aqueous solution)
As a reducing agent contained in the second aqueous solution, formaldehyde, sodium erythorbate borohydride, hydrazine, hydrazine compound, hydroquinone, L-ascorbic acid, L-ascorbate, formic acid, anhydrous sodium sulfite, L (+) tartaric acid, formic acid A single type of ammonium, longalite, pyrocatechol, or a combination of two or more types may be used.
Of these reducing agents, it is more preferable to use L-ascorbic acid or a combination of L-ascorbic acid and pyrocatechol because the reduction reaction to silver nitrate can be easily controlled.

Moreover, it is preferable that the compounding quantity of the silver nitrate reducing agent in the second aqueous solution is usually within a range of 0.5 to 20% by weight.
The reason for this is that when the amount of the reducing agent is less than 0.5% by weight, the production rate of the flaky silver powder is excessively reduced, and the production efficiency may be significantly reduced.
On the other hand, if the amount of the reducing agent exceeds 20% by weight, it may not be dissolved in water.
Therefore, the amount of the reducing agent contained in the second aqueous solution is more preferably set to a value within the range of 4 to 18% by weight, and further preferably set to a value within the range of 7 to 15% by weight.

Nitric acid can also be blended in the first aqueous solution as described above, but when blending nitric acid as a form control agent in the second aqueous solution, the blending amount is based on the total amount of the second aqueous solution. The value is preferably 20% by weight or less.
That is, when the amount of nitric acid exceeds 20% by weight, a plurality of minute protrusions may grow abnormally as a surface state on the surface (front surface and back surface) of the flaky silver powder.
However, if the amount of the organic acid is excessively reduced, the effect of addition may not be exhibited stably.
Therefore, it is more preferable to set the blending amount of nitric acid to a value within the range of 0.1 to 10% by weight, and a value within the range of 0.5 to 5% by weight with respect to the total amount of the second aqueous solution. More preferably.

In addition, as described above, the organic acid can be blended in the first aqueous solution, but when blending the organic acid as the form control agent in the second aqueous solution, the blending amount is adjusted to the total amount of the second aqueous solution. On the other hand, the value is preferably 2% by weight or less.
That is, when the blending amount of the organic acid exceeds 2% by weight, the shape of the silver powder is not flaky but may be almost spherical.
However, if the amount of the organic acid is excessively reduced, the effect of addition may not be exhibited stably.
Therefore, it is more preferable that the blending amount of the organic acid is a value within the range of 0.001 to 0.5% by weight with respect to the total amount of the second aqueous solution. More preferably, the value is within the range.

As described above, ammonia or the like can be blended in the first aqueous solution, but when blending ammonia or the like as a form control agent in the second aqueous solution, the blending amount is adjusted to the total amount of the second aqueous solution. On the other hand, the value is preferably 2% by weight or less.
That is, if the amount of ammonia or the like exceeds 2% by weight, the particle size of the silver powder may be too small.
However, when the amount of ammonia or the like is excessively small, the mixing effect cannot be obtained, and it may be difficult to control the average particle size.
Therefore, it is more preferable to set the blending amount of ammonia or the like to a value within the range of 0.1 to 1.5% by weight with respect to the total amount of the second aqueous solution, and within the range of 0.5 to 1% by weight. More preferably, it is a value.

  Also, the amount of water (ion-exchanged water) should be the remaining amount of silver nitrate reducing agent, nitric acid, organic acid, ammonia water, etc., and the total amount of the second aqueous solution comprising these components should be 100% by weight. preferable.

Therefore, as a blending example of the second aqueous solution, a silver nitrate reducing agent, nitric acid, an organic acid, and water are blended, respectively, and the total amount (100 wt%) of the second aqueous solution is silver nitrate. The amount of the reducing agent is within the range of 0.5 to 20% by weight, the amount of nitric acid is 20% or less, the amount of organic acid is 2% or less, and the remaining amount It is preferable to use water.
As another blending example of the second aqueous solution, a silver nitrate reducing agent, nitric acid, an organic acid, ammonia, and water are blended, and the total amount of the second aqueous solution (100 wt. %), The amount of silver nitrate reducing agent is within the range of 0.5 to 20% by weight, the amount of nitric acid is 20% by weight or less, and the amount of organic acid is 2% by weight or less. It is preferable that the value and the blending amount of ammonia, etc. are 2% by weight or less and the remaining amount of water.
In addition, as described above, nitric acid, aqueous ammonia, and organic acid can be blended in the first aqueous solution. In this case, the blending amount of nitric acid, aqueous ammonia, and organic acid in the second aqueous solution, It can be changed as appropriate.

(Reaction temperature)
Moreover, it is preferable to make the reaction temperature at the time of implementing a reduction process, ie, the reaction temperature of 1st aqueous solution and 2nd aqueous solution, the value below 60 degreeC.
This is because it may be difficult to control the shape and average particle size of the flaky silver powder when the reaction temperature is 60 ° C. or higher.
On the other hand, when the reaction temperature is less than 0 ° C., ice may be precipitated, or the amount of flaky silver powder deposited may be significantly reduced, thereby reducing the productivity of flaky silver powder.
Accordingly, the reaction temperature is more preferably set to a value within the range of 10 to 50 ° C, and further preferably set to a value within the range of 20 to 40 ° C.

(surface treatment)
The obtained flaky silver powder is preferably subjected to a surface treatment with at least one of an organic acid (including an organic acid salt), for example, stearic acid, myristic acid, calcium stearate, calcium myristate, and the like.
More specifically, it is preferable to put the organic acid salt aqueous solution as it is into a container that has been subjected to the liquid phase reduction method, and to perform surface treatment with an organic acid on the obtained flaky silver powder.
The reason for this is that, by performing surface treatment with an organic acid, the shape retention of the flaky silver powder is remarkably improved, and the non-flaky silver powder easily enters the gap between the horizontally oriented flaky silver powders. This is because it becomes easy to control the value of the specific resistance within a desired numerical range.
Moreover, when using an organic acid, it is also preferable to perform surface treatment by washing the silver powder with water, substituting the alcohol, and introducing an alcohol solution of the organic acid.
In addition, when carrying out the surface treatment with an organic acid for the flaky silver powder, the treatment amount of the organic acid or the organic acid salt is within the range of 0.001 to 5 parts by weight with respect to 100 parts by weight of the flaky silver powder. It is preferable to use a value.
The reason for this is that by adjusting the treatment amount of the organic acid in this way, the balance between the shape retention of the flaky silver powder and the specific resistance is further improved.
Therefore, it is more preferable that the treatment amount of the organic acid is set to a value within the range of 0.01 to 1 part by weight with respect to 100 parts by weight of the flaky silver powder, and within a range of 0.05 to 0.5 part by weight. More preferably, the value of

(Drying process)
Moreover, it is preferable to heat-process by providing a drying process with respect to the flaky silver powder which performed predetermined surface treatment.
That is, for example, it is preferable to heat-treat at a temperature of 30 ° C. or higher for 30 minutes or more after performing a predetermined surface treatment on the flaky silver powder obtained by the wet reduction method.
The reason for this is that the heat treatment can effectively disperse the liquid remaining inside the flaky silver powder, such as water, and as a result, the shape retention of the flaky silver powder can be remarkably improved. Because. In other words, if the flaky silver powder obtained by the liquid phase reduction method is left as it is in a wet state, the shape of the flaky silver powder tends to collapse.
Therefore, in order to obtain more excellent shape retention, it is preferable to perform heat treatment at a temperature of 40 to 150 ° C. for about 1 to 48 hours using a vacuum oven or a thermostatic bath.

(2) (a2) Non-flaky silver powder As the non-flaky silver powder, the average particle diameter is a value in the range of 1 to 5 μm, and the bulk density is a value in the range of 0.3 to ³ g / cm ^3. It is characterized by being.
That is, (A) As a part of the silver powder, a predetermined non-flaky silver powder is used in combination with the predetermined flaky silver powder to horizontally align the gaps between the vertical and adjacent flaky silver powders. It is because it becomes easy to form the silver-powder laminated structure in which non-flaky silver powder penetrates.
Therefore, in a wide range of blending amounts of these silver powders, a film with a relatively large area (conductive layer) that can exhibit good shielding properties and has good followability and adhesion to an electronic substrate on which an electric element is mounted. ) Can be easily formed.

(3) Mixing ratio of flaky silver powder / non-flaky silver powder In constituting the conductive paste, the mixing ratio (weight ratio) of flaky silver powder and non-flaky silver powder is 80:20 to 40:60. A value within the range is preferable.
The reason for this is that with such a blending ratio, the film formability is improved, the adhesion to the electronic substrate, the follow-up to the three-dimensional unevenness due to the electronic element, etc., further, This is because it becomes easy to balance with good shielding characteristics.
More specifically, when the blending ratio (weight ratio) between the flaky silver powder and the non-flaky silver powder is greater than 80:20, the existing ratio of the non-flaky silver powder decreases, and the silver powder laminated structure in the conductive layer This is because the formation of is insufficient, the conductivity in the thickness direction (vertical direction) and the like is lowered, and as a result, the shield characteristics may be lowered.
On the other hand, when the blending ratio (weight ratio) between the flaky silver powder and the non-flaky silver powder is smaller than 40:60, the existing ratio of the flaky silver powder is decreased, and the formation of the silver powder laminated structure in the conductive layer is insufficient. Similarly, the conductivity in the plane direction (horizontal direction) is lowered, and as a result, the shield characteristics may be lowered.
Therefore, it is more preferable to set the blending ratio (weight ratio) between the flaky silver powder and the non-flaky silver powder to a value within the range of 75:25 to 45:55, and within the range of 70:30 to 50:50. More preferably, it is a value.

3. (B) Binder resin (1) Type 1
The binder resin preferably includes at least one electrically insulating resin selected from the group consisting of an epoxy resin, a phenol resin, a thermosetting acrylic resin, a thermosetting urethane resin, and a silicone resin.
By using such a resin, good adhesion characteristics to an electronic substrate, an electronic element, etc. can be obtained, and good shielding characteristics and conductivity can be maintained even when environmental characteristics have changed greatly. Because it can.

Further, when the binder resin is an epoxy resin or the like, it is preferable to blend a predetermined amount of a curing agent in order to obtain good adhesion and mechanical strength.
Examples of such a curing agent include one or a combination of two or more of an imidazole compound, a secondary amine compound, a tertiary amine compound, a modified aliphatic amine compound, and an epoxy resin amine adduct compound.
In particular, an imidazole compound is a preferable curing agent because it has a high potential at room temperature and has a wide reaction temperature range of 80 to 170 ° C.
In addition, as a commercial item of an imidazole compound, 2P4MHZ-PW, C-11Z, C-17Z (above, Shikoku Chemicals Co., Ltd. product), 2-phenylimidazole, 1-benzyl-2-methylimidazole (above) , Nippon Synthetic Chemical Co., Ltd.).

Moreover, it is preferable that the addition amount of this hardening | curing agent shall be a value within the range of 3-40 weight part with respect to 100 weight part of epoxy resins.
The reason for this is that when the amount of the curing agent added is less than 10 parts by weight, the curing becomes insufficient and the adhesive properties may be significantly deteriorated.
On the other hand, when the addition amount of the curing agent exceeds 40 parts by weight, the conductivity may be lowered or the potential may be lowered.
Therefore, it is more preferable that the addition amount of the curing agent is a value within the range of 5 to 30 parts by weight, and a value within the range of 7 to 20 parts by weight with respect to 100 parts by weight of the epoxy resin. Is more preferable.
In addition, the weight part of the epoxy resin which determines the addition amount of a hardening | curing agent means the total amount after also including that, when a reactive diluent is included.

(2) Type 2
Moreover, it is preferable that the binder resin contains at least one thermoplastic resin selected from the group consisting of a polyester resin, a polyolefin resin, a polyamide resin, and a polyurethane resin.
The reason for this is that by including such a thermoplastic resin, predetermined adhesive properties can be obtained, and in the case where a failure occurs in the electrical properties between the adherends, they can be easily repaired. Because.
In addition, when these resins are used, the film formability is further improved, the followability to three-dimensional irregularities caused by electronic elements and the like is improved, and furthermore, a good balance with the shielding characteristics can be achieved. This is because it becomes easy.

(3) Diluent It is also preferable to mix a diluent (including a reactive diluent) as part of the binder resin.
Examples of such a diluent include one or a combination of two or more of an aliphatic monofunctional epoxy compound, an aliphatic bifunctional epoxy compound, an aromatic monofunctional epoxy compound, and the like.
More specifically, o-sec-butylphenyl glycidyl ether, cyclohexane dimethylol type epoxy resin, phenyl glycidyl ether, o-cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, o-phenylphenyl glycidyl ether , Nonylphenyl glycidyl ether, phenol (EO) ₅ glycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,6-hexanediol di Glycidyl ether, 1,4-butanediol diglycidyl ether, 2-ethylhexyl glycidyl ether Or a combination of two or more thereof.

Moreover, it is preferable to make the addition amount of a diluent into the value within the range of 5 to 30 weight% with respect to the whole quantity of binder resin.
The reason for this is that if the amount of the diluent added is less than 5% by weight, the effect of addition may not be obtained.
On the other hand, when the amount of the diluent added is 30% by weight or more, the adhesion to an electronic substrate or the like may be significantly reduced.
Therefore, it is more preferable that the addition amount of the diluent is a value within the range of 8 to 25% by weight, and a value within the range of 10 to 22% by weight with respect to the total amount of the binder resin. Further preferred.

(4) Various additives Various additives such as antioxidants, ultraviolet absorbers, metal ion scavengers, viscosity modifiers, inorganic fillers, organic fillers, carbon fibers, colorants, and couplings in the conductive paste. It is also preferable to add an agent or the like.
In particular, the conductive paste usually accelerates the oxidative deterioration due to the addition of a metal such as flaky silver powder. Therefore, as an antioxidant, an amine-based antioxidant, a phenol-based antioxidant, or a phosphate ester-based oxidation is used. It is preferable to add an inhibitor or the like within a range of 0.1 to 10% by weight with respect to the total amount of the conductive paste.

4). (C) Solvent Further, in constituting the conductive paste, various organic solvents can be blended as the (C) solvent, but the solubility parameter (SP value) is a value within the range of 8.0 to 11.0. In addition, the boiling point is preferably set to a value within the range of 70 to 180 ° C.
The reason for this is that by using such a solvent, the handleability of the resulting conductive paste can be improved and the film formability can be further improved, and as a result, a balance with good shielding properties. It is because it becomes easy to take.
In addition, although the compounding quantity of a solvent can be defined considering the use of a conductive paste, usability, etc., it is usually taken as the value within the range of 10-100 weight part with respect to 100 weight part of silver powder. preferable.
The reason for this is that when the amount of the solvent is less than 10 parts by weight, the viscosity increases, and the mixed dispersion of the silver powder, the binder resin, and the solvent becomes non-uniform, or the solvent is separated when forming the stirred coating film. This is because it may worsen and cause voids (residual bubbles).
On the other hand, when the amount of the solvent is larger than 100 parts by weight, the viscosity is lowered, silver powder is likely to be precipitated, and it may be difficult to handle the conductive paste.
Therefore, the blending amount of the solvent is more preferably set to a value within the range of 20 to 70 parts by weight, and further preferably set to a value within the range of 25 to 50 parts by weight with respect to 100 parts by weight of the silver powder.

5. Various characteristics (1) Specific resistance In addition, flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15) of a predetermined amount (when the amount of silver powder is 100 parts by weight with respect to 100 parts by weight of binder resin) The specific resistance of the cured product of the conductive paste is preferably set to a value of 1 × 10 Ohm · cm or less.
The reason for this is that when the specific resistance of the cured product of the conductive paste exceeds 1 × 10 Ohm · cm, the conduction resistance increases. In particular, the shielding characteristics at the corners of the electronic element are not evenly exhibited. It is because there is a case to do.
However, if the specific resistance of the cured conductive paste is too small, the types of flaky silver powder and non-flaky silver powder that can be used are excessively limited, or the silver content is excessively high. This is because the formation of the film becomes insufficient, the coating film becomes brittle, and furthermore, the conduction may be poor.
Therefore, it is more preferable to set the specific resistance of the cured conductive paste to a value in the range of 5 × 10 ⁻⁵ to 1 × 10 ⁻² Ohm · cm, and 1 × 10 ⁻⁴ to 1 × 10 ⁻³ Ohm. -More preferably, the value is within the range of cm.
The specific resistance of the conductive paste comprising a predetermined amount of flaky silver powder can be measured by the four-terminal method shown in Example 1 after being cured under predetermined conditions, as will be described later.

Here, referring to FIG. 6, the relationship between the two types of silver powder concentrations (wt%) and the specific resistance (Ohm · cm) will be described.
That is, in FIG. 6, the characteristic curve A corresponds to the specific resistance in the cured product of the conductive paste when flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15) is used. B respond | corresponds to the specific resistance in the hardened | cured material of an electrically conductive paste at the time of using only flaky silver powder.
And except the silver powder density | concentration in an electrically conductive paste, it is based on the aspect of Example 1 mentioned later fundamentally.
As understood from the characteristic curve A, the specific resistance of the obtained conductive cured product decreases as the total amount of flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15) increases. For example, when the total blending amount is 25% by weight, the specific resistance is about 1.0 × 10 ¹ Ohm · cm. When the total blending amount is 30% by weight, the specific resistance is 3 × 10 ⁻² Ohm.・ It dropped rapidly with cm. In addition, when the total amount is 40% by weight, the specific resistance decreases to 9.0 × 10 ⁻⁴ Ohm · cm, and when the total amount is 50 to 70% by weight, the specific resistance is about 1.1 × 10. ^{-4 to} 2.8 × 10 ⁻⁴ Ohm · cm, which is a substantially constant low value.
On the other hand, as understood from the characteristic curve B, even when the flaky silver powder is used alone, the specific resistance (Ohm · cm) of the obtained conductive cured product tends to decrease as the blending amount increases. It was. However, when the blending amount is in the range of 25% to 30% by weight, the specific resistance (Ohm · cm) is almost the same as that of the characteristic curve A, but when the blending amount is in the range of more than 30% to 70% by weight. The specific resistance value tended to be clearly higher than the specific resistance characteristic curve A.

(2) Shielding property Further, a conductive paste comprising a predetermined amount (a ratio of 100 parts by weight with respect to 100 parts by weight of the binder resin) of flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15). It is preferable that the shield property measured in accordance with the KEC method of the cured product is a value of 20 db or more.
This is because, when the shield property of the cured product of the conductive paste is less than 20 db, for example, the shield property at the corner of the electronic device may not be exhibited, and the electronic device may malfunction. is there.
However, if the shielding properties of the cured conductive paste is excessively large, the types of flaky silver powder and non-flaky silver powder that can be used are excessively limited, or the silver content is excessively high. Insufficient formation of the film may cause the coating film to become brittle or poor conductivity.
Therefore, it is preferable to set the shield characteristic of the cured product of the predetermined conductive paste to a value in the range of 50 to 150 dB, and more preferably to a value in the range of 65 to 100 dB.
In addition, the shield characteristic of the hardened | cured material of a predetermined conductive paste can be measured based on the KEC method shown in Example 1, after making it harden | cure on predetermined conditions so that it may mention later.

Here, referring to FIG. 7, the relationship between the two types of silver powder concentrations (% by weight) and the shield characteristics will be described.
That is, in FIG. 7, the characteristic curve A corresponds to the shield characteristic in the cured product of the conductive paste when using flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15). B respond | corresponds to the shielding characteristic in the hardened | cured material of the electrically conductive paste at the time of using only flaky silver powder.
And except the silver powder density | concentration in an electrically conductive paste, it is based on the aspect of Example 1 mentioned later fundamentally.
As understood from the characteristic curve A, the larger the total amount of flaky silver powder / non-flaky silver powder (weight blend ratio = 35: 15), the greater the shield property value of the obtained conductive cured product. For example, when the total blending amount is 25% by weight, the shielding property is about 15 dB. When the total blending amount is 30% by weight, the shielding property rapidly increases to about 32 dB. Further, when the total blending amount was 40% by weight, the shielding characteristics increased to about 57 dB, and when the total blending amount was 50 to 70% by weight, the shielding characteristics showed a high attenuation value of about 68 to 78 dB.
On the other hand, as understood from the characteristic curve B, even when the flaky silver powder was used alone, the value of the shielding property of the obtained conductive cured product tended to increase as the blending amount increased. However, even if the blending amount is in the range of 25 wt% to 30 wt%, the value of the shielding property obtained is small compared to the characteristic curve A, and the blending amount is in the range of more than 30 wt% to 75 wt%. Even so, there was a tendency that the value of the shield characteristic was lower than that of the characteristic curve A.

(3) Viscosity Further, the viscosity of the conductive paste is preferably set to a value within the range of 1 to 100 Pa · sec (temperature: 25 ° C.), and more preferably set to a value within the range of 10 to 50 Pa · sec. .
The reason for this is that when the viscosity is less than 1 Pa · sec, it spreads out after applying the paste, the prescribed film thickness cannot be controlled, silver powder tends to settle, and uneven coating occurs. This is because the performance may be significantly impaired.
On the other hand, when the viscosity is 100 Pa · sec or more, the applicability by dispensing, printing, or the like is extremely deteriorated, and the adhesion and conductive performance may be deteriorated.

(4) Density Moreover, it is preferable to make the density of an electrically conductive paste into the value within the range of 1-3.5 g / cm < ³ >.
The reason for this is that when the density of the conductive paste is less than 1 g / cm ³ , silver powder concentration unevenness is likely to occur when applied to an adherend, and the shield characteristics and adhesion may be significantly reduced. Because there is.
On the other hand, even if the density of the conductive paste exceeds 3.5 g / cm ³ , the concentration unevenness of the silver powder similarly increases, and it may be difficult to obtain stable shield characteristics and adhesion. It is.
Therefore, the density of the conductive paste, it is more preferably a value within the range of 1.2~3g / cm ^3, still more preferably a value within the range of 1.5~2.5g / cm ³ .
In addition, since the conductive paste of the present invention uses flaky silver powder or non-flaky silver powder having a very low bulk density, the blending amount is adjusted, or the type and blending amount of the binder resin are appropriately changed. Can be adjusted to a desired range.

7). Production method The production method of the conductive paste is not particularly limited. For example, using a propeller mixer, a planetary mixer, a triple roll, a kneader, a spatula, etc. The flaky silver powder and non-flaky silver powder are preferably produced by uniformly mixing and dispersing.
For example, when a planetary mixer is used, it is understood that a conductive paste showing a certain specific resistance is obtained after curing if the mixing time is in the range of 10 to 120 minutes.
In addition, it is preferable that once the conductive paste is manufactured, aggregates and dust are filtered and removed using a filter or the like.
This is because the conductive paste is applied by using a dispenser, a spray coating device, or the like, or laminated by screen printing or an ink jet method by filtering the aggregates of the flaky silver powder and the non-flaky silver powder. This is because it is possible to effectively prevent clogging of eyes.
In addition, if it is a flaky silver powder of the present invention, it is flaky and easily deformed, so when mixed in a binder resin, there is little occurrence of aggregates, for example, with an aperture of 40 to 180 μm. There is an advantage that it can be easily filtered using a mesh filter or the like.

8). Usage method The usage method of the conductive paste is not particularly limited. For example, a dispenser coating device, a spray coating device, a resin film, a conductive film, or an electronic substrate equipped with an electronic element. It is preferable that a conductive paste is laminated by using a screen printing apparatus or an inkjet apparatus, thereby forming a conductive layer having a predetermined thickness, thereby forming an electromagnetic wave shielding member that can be thermally cured.
More specifically, as shown in FIG. 8, the conductive paste of the present invention is applied to a predetermined thickness on the surface of an electronic substrate 20 on which a plurality of molded electronic elements 22 are mounted, The conductive layer 18 is formed by heat curing or the like, and thus the electronic device 10 including the shielded electronic substrate 20 can be obtained.
Therefore, as an example, when using the conductive paste, first, a heat-resistant release film of 25 to 75 μm is prepared.
Next, a conductive paste is laminated on the heat-resistant release film using a dispenser coating device or the like so that the thickness after drying becomes a value within the range of 10 to 100 μm.
Next, the conductive paste is heated using a heating oven, an infrared lamp, or the like under heating conditions of 100 ° C. or lower and about 1 to 10 minutes to obtain an electromagnetic wave shielding member in which the binder resin is partially cured.
Next, a heat-resistant release film including an electromagnetic wave shielding member that is partially cured is laminated on an electronic substrate on which a semiconductor element or the like is mounted using a laminating apparatus.
Next, the heat-resistant release film is peeled off, leaving only the electromagnetic wave shielding member that is flexible and partially cured.
Finally, the electromagnetic shielding member laminated on the whole or part of the electronic substrate is again heated under a heating condition of 140 to 180 ° C. for 20 to 60 minutes using a heating oven or an infrared lamp. It can be set as the electroconductive layer excellent in adhesiveness and a shield characteristic formed by processing and hardening binder resin.

[Second Embodiment]
The second embodiment is an electromagnetic wave shielding member obtained by processing the conductive paste of the first embodiment into a film shape.
Hereinafter, the electromagnetic wave shielding member of the second embodiment will be specifically described with reference to the drawings as appropriate.

1. Conductive paste Since the content is the same as that described in the first embodiment, the description thereof is omitted.

2. Film-like material (1) Thickness Although the thickness of the film-like material, that is, the thickness of the conductive paste in the case of the conductive layer (conductive film-like material) can be changed according to the usage, etc. Usually, it is preferable to set it as the value within the range of 10-200 micrometers.
The reason for this is that when the thickness of the film-like material is less than 10 μm, it may be difficult to handle and produce a uniform thickness, and the three-dimensional followability to surface irregularities can be obtained. This is because there may be a problem that the shield characteristics are likely to be poor.
On the other hand, when the thickness of such a film-like material exceeds 200 μm, on the contrary, it may be difficult to handle and produce a uniform thickness, and the cost is increased, which tends to be economically disadvantageous. Because.
Therefore, the thickness of the film-like product is more preferably set to a value within the range of 30 to 150 μm, and further preferably set to a value within the range of 50 to 100 μm.

(2) Size / Shape / Form Although the size and shape of the film-like material can be changed according to the intended use, etc., usually the front and back surfaces of the substrate on which the electronic element is mounted, or either It is preferable that the size or shape covers either one of them entirely or partially.
Therefore, for example, when the size of the electronic substrate is 1.0 × 1.0 cm ² and the shape is a square, the size of the film-like material is 1.0 × A square in the range of 1.0 cm ^{2 to} 1.2 × 1.2 cm ² is preferable.
However, in the case of a semiconductor element related to the malfunction of the electromagnetic wave shield, the size of the film-like object having an area of 100% to 150% of the projected area when they are viewed in plan is individually covered. In addition, the shape is preferably rectangular, square, circular, elliptical, irregular, or the like.
Furthermore, in the substrate on which the electronic element is mounted, the predetermined element is retrofitted, then electric wiring is performed, the predetermined element is excessively high, and the predetermined element is covered with another shielding material. In consideration of the case, it is also preferable that the portion has a perforated structure corresponding to the predetermined element.

[Example 1]
1. Production of conductive paste (1) Preparation of flaky silver powder First, a first aqueous solution containing silver nitrate, ion-exchanged water, an organic acid, and nitric acid was prepared.
That is, in a container with a stirrer (container A), 4 g of silver nitrate, 24 g of ion-exchanged water, 0.02 g of citric acid (citric acid monohydrate), 2 g of nitric acid (concentration: 69% by weight), And stirred using a magnetic stirrer until uniform.
Next, a second aqueous solution containing a reducing agent and ion-exchanged water was prepared.
That is, 3 g of L-ascorbic acid as a reducing agent and 24 g of ion-exchanged water were accommodated in another container (container B) with a stirrer, and stirred using a magnetic stirrer until uniform.
And after hold | maintaining temperature so that each liquid temperature may be 30 degreeC, the 2nd aqueous solution of the container B is added with respect to the 1st aqueous solution in the container A, and stirring is continued as it is, and flaky silver powder is precipitated and produced. It was.

Next, the precipitated flaky silver powder is washed with ion-exchanged water, and then a predetermined amount of the organic acid is treated at a ratio of 0.02 parts by weight with respect to 100 parts by weight of the flaky silver powder. An aqueous ammonium stearate solution (0.5 wt%) was added to the mixed solution, and surface treatment with an organic acid was performed.
Thereafter, the flaky silver powder subjected to the surface treatment is drained by filtration, and further dried using a vacuum oven at 100 ° C. for 3 hours to obtain flaky silver powder (a1-1, average particle diameter ( D ₅₀ ): 15 μm, bulk density: 1.4 g / cm ³ ).

(2) Preparation of non-flaky silver powder As non-flaky silver powder (a2-1), chestnut-like silver powder (made by Kaken Tech Co., Ltd., special shape silver powder for conductive adhesive TK paste CR-2800, average particle diameter (D ₅₀ ): 3.0 μm, bulk density: 1.6 g / cm ³ ) was prepared by a general wet reduction method of silver chloride.

(3) Preparation of binder resin In a container equipped with a stirrer, 100 g of propylene glycol monomethyl ether acetate having a solubility parameter (Fedors method) of 9.2 and a boiling point of 146 ° C., a number average molecular weight of 11.000, and a hydroxyl value And a polyester resin (BC1) having a solid content concentration of 50% by weight was prepared as a binder resin.
Next, 33 g of the propylene glycol monomethyl ether acetate described above and 67 g of urethane acrylic resin having a number average molecular weight of 1,400 and having acrylate residues at both ends are contained in a separate container with a stirrer, and uniformly The mixture was stirred until 0.1 g of benzoyl peroxide as a polymerization initiator was blended to prepare a urethane acrylic resin solution (BC2) having a solid concentration of 67% by weight.
Then, in another container (1 liter) with a stirrer, 35 g of EPICLON 830-S (bisphenol F type, manufactured by Dainippon Ink & Chemicals), 10 g of butylphenyl glycidyl ether as a reactive diluent, and a curing agent, 5 g of cure sol 2p4MHZ-PW (manufactured by Shikoku Kasei Kogyo), 20 g of the above-described polyester solution (BC1) and 20 g of the above-mentioned urethane acrylate resin solution (BC2) were accommodated, mixed and stirred for 15 minutes, and uniformly After obtaining the solution, 6 g of propylene glycol monomethyl ether acetate was added and blended to obtain a binder resin (R1, solid content 73.4% by weight) containing a solvent.

(4) Preparation of conductive paste In a planetary mixer-container, 48 g of binder resin (R1) containing the solvent described above (solid content conversion: 36.7 g) and flaky silver powder (a1-1) 35 g And 15 g of non-flaky silver powder (a2-1), and then stirred for 30 minutes or more until the blended raw material of the conductive paste became uniform.
Next, after passing three rolls (roll interval 30 to 40 μm) twice, 2 g of an additional organic solvent was added, and the mixture was again returned to the planetary mixer-container and further stirred and mixed for 30 minutes. In Table 1, the total amount of the solvent in R1 and the solvent added after passing through the three rolls is shown as c1.
Subsequently, after defoaming for 5 minutes under a reduced pressure condition of -0.1 MPa · G, filtration treatment was performed using a filtration device equipped with a mesh filter having an opening of 63 μm to obtain the conductive paste of Example 1. .

2. Evaluation of conductive paste (1) Viscosity (Evaluation 1)
After adjusting the temperature of the conductive paste in the sample cup to 25 ° C. using a temperature controller (circulating water bath) connected in advance to the sample cup, E-type viscometer VISCOMETER TV22 (manufactured by Toyo Sangyo Co., Ltd.) Was used, and the viscosity of the conductive paste was measured under high rotation conditions (5 rpm) and evaluated in light of the following criteria. The obtained evaluation results are shown in Table 1.
A: A value within a range of 15 to 30 Pa · sec.
A: Less than 10-15 Pa · sec, or a value in the range of more than 30-50 Pa · sec.
(Triangle | delta): It is a value within the range of less than 10-10 Pa.sec or more than 50-100 Pa.sec.
X: A value of less than 1 Pa · sec or more than 100 Pa · sec.

(2) Thixo coefficient (Evaluation 2)
Next, the viscosity of the conductive paste was measured under low rotation conditions (0.5 rpm), and the thixotropic coefficient was calculated from the ratio with the viscosity obtained in Evaluation 1, and evaluated in light of the following criteria. The obtained evaluation results are shown in Table 1.
(Double-circle): It is a value within the range of 3-5.
A: A value in the range of 2.5 to less than 3, or more than 5 to 6 or less.
(Triangle | delta): It is a value within the range of less than 2-2.5 or more than 6-7.
X: A value of less than 2.0 or more than 7.0.

(3) Density (Evaluation 3)
The density of the obtained conductive paste was measured according to JIS K 7383 and evaluated according to the following criteria. The obtained evaluation results are shown in Table 1.
(Double-circle): It is a value within the range of 2.0-2.5.
○: It is a value within the range of less than 1.5-2 or more than 2.5-3.
(Triangle | delta): It is a value within the range of less than 1-1.5 or more than 3 -3.5.
X: A value less than 1.0 or more than 3.5.

(4) Applicability (Evaluation 4)
The obtained conductive paste was screen-printed in a line shape (length 60 mm × width 20 mm × thickness 80 μm) on a glass plate having a thickness of 8 mm, and then heat-cured at 160 ° C. for 60 minutes, From the state of the conductive layer as the obtained coating film, etc., the coating property was evaluated according to the following criteria.
A: Uniform silver luster visually, and high surface smoothness by touch.
○: Although there is a little uniform silver luster visually, the surface smoothness due to finger touch is high.
(Triangle | delta): There is no uniform silver luster visually and there is a rough feeling of the surface by finger touch.
X: A film cannot be formed as a conductive layer having a uniform thickness.

(5) Adhesion (Evaluation 5)
The obtained conductive paste was applied to a thickness of 50 μm on a glass epoxy substrate having a length of 100 mm × width of 25 mm × thickness of 1.5 mm using a spacer and a coating rod.
Next, after heating and curing at 160 ° C. for 60 minutes and returning it to room temperature, 100 squares with 1 mm intervals were prepared according to the cross cut test method (JIS K5600-4-6), and an adhesive tape The number of masses to be peeled was measured, and the adhesion was evaluated from the peel rate according to the following criteria.
A: The value is 1% or less.
A: A value of 5% or less and outside the above range.
(Triangle | delta): It is a value of 10% or less, and is outside the said range.
X: A value exceeding 10%.

(6) Specific resistance (Evaluation 6)
The specific resistance of the obtained conductive paste was measured. That is, the conductive paste was printed on a glass plate in a line shape (length: 40 mm, width: 1 mm, thickness: 80 μm) using screen printing, and further heat-cured under conditions of 160 ° C. × 30 minutes. Later, the resistance between two points was measured by the four probe method, the specific resistance was calculated, and evaluated according to the following criteria. The obtained evaluation results are shown in Table 1.
A: Value of 5 × 10 ⁻⁴ Ohm · cm or less.
○: 1 × 10 ⁻² Ohm · cm or less and out of the above range.
Δ: A value of 1 × 10 Ohm · cm or less and outside the above range.
×: It is a value exceeding 1 × 10 Ohm · cm.

(7) Shield characteristics (Evaluation 7)
In a state where a heat-resistant polyester film (length: 300 mm × width: 200 mm × thickness: 120 μm) is temporarily fixed on a glass plate having a thickness of 8 mm, a rectangular film (length: 200 mm) is formed thereon using a spacer and a coating rod. X width 150 mm x thickness 80 μm), and then cured by heating at 160 ° C. for 60 minutes.
Next, from the rectangular film-like product, a long product (140 mm long × 120 mm wide) was cut out to obtain a test piece for shielding properties.
Next, in accordance with the KEC method, shield characteristics were measured in a frequency range of 100 KHz to 1 GHz using a shield measuring device N9000A (manufactured by Agilent Technologies). The measured value was calculated by the following formula, graphed as shield performance (SE), and shield performance at a frequency of 500 MHz was evaluated according to the following criteria.
The obtained evaluation results are shown in Table 1. In addition, in FIG. 9, the shield characteristic chart in Example 1 is shown.
SE = −20 log (E ₀ / E _i )
E _i : Incident electric field (V / m)
E ₀ : Transmission electric field (V / m)
A: A value of 70 dB or more.
A: A value of 50 dB or more and outside the above range.
Δ: A value of 20 dB or more and outside the above range.
X: The value is less than 20 dB.

(8) Silver powder laminate structure (evaluation 8)
In the evaluation 5, the sample used for the adhesion measurement was cured in a state of being embedded in an epoxy resin for creating a cut sample.
Next, after cutting with a diamond cutter and polishing the cut surface, an electron micrograph of the cross-section of the conductive layer was observed, and then the formability of the silver powder laminate structure was determined according to the following criteria.
(Double-circle): The silver powder laminated body structure is formed notably.
◯: Although the flaky silver powder has some poor horizontality, the silver powder laminate structure is clearly formed.
(Triangle | delta): Although the horizontality of flaky silver powder is partially poor, the silver powder laminated body structure is partially formed.
X: The flaky silver powder has poor horizontality, and the silver powder laminate structure is not formed.

[Examples 2 to 5]
In Examples 2-5, as shown in Table 1, the compounding quantity of flaky silver powder (a1-1) and non-flaky silver powder (a2-1) is 37g / 13g (Example 2), 32.5g / Except for 17.5 g (Example 3), 31 g / 18 g (Example 4), and 24 g / 26 g (Example 5), a conductive paste was prepared in the same manner as in Example 1, and the shield characteristics and the like were the same. Measured. The evaluation results obtained are shown in Table 1.

[Comparative Examples 1-3]
In Comparative Examples 1-3, as shown in Table 1, the blending amounts of the flaky silver powder (a1-1) and the non-flaky silver powder (a2-1) were 0 g / 50 g (Comparative Example 1), 15 g / 35 g ( Except for using Comparative Example 2) and 45 g / 5 g (Comparative Example 3), a conductive paste was prepared in the same manner as in Example 1, and the shield characteristics and the like were measured in the same manner. The evaluation results obtained are shown in Table 1.
In addition, in FIG. 10, the shield characteristic chart in the comparative example 1 is shown.

Note 1: Converted to solid content in R1 (g)
Note 2: Total weight (g) of solvent in R1 and solvent added after passing three rolls
Evaluation 1: Viscosity evaluation 2: Thixo coefficient evaluation 3: Density evaluation 4: Coating property evaluation 5: Adhesion evaluation 6: Resistivity evaluation 7: Shield property evaluation 8: Silver powder laminate structure

[Examples 6 to 8]
In Examples 6-8, when preparing the 2nd aqueous solution in Example 1, the compounding quantity etc. of nitric acid were changed, and the influence with respect to the bulk density and average particle diameter of flaky silver powder was examined.
That is, in Example 6, 1.4 g of nitric acid was mixed with the first aqueous solution and 0.6 g of the second aqueous solution, and 0.02 g of organic acid (citric acid monohydrate) and 4 g of L-ascorbic acid were added to the second aqueous solution. While blended in an aqueous solution, the reaction temperature was set to 30 ° C. to obtain a flaky silver powder (a1-2, average particle diameter: 26.5 μm, average thickness: 0.1 μm, bulk density: 1.3 g / cm ³ ). Except for the above, a conductive paste was produced and evaluated in the same manner as in Example 1.
In Example 7, 2 g of nitric acid, 0.04 g of organic acid (citric acid monohydrate) and 4 g of L-ascorbic acid were added to the second aqueous solution, respectively, and the reaction temperature was 20 ° C. (A1-3, average particle diameter: 25.3 μm, average thickness: 0.1 μm, bulk density: 1.0 g / cm ³ ) was obtained.
In addition, as a flaky silver powder having a different particle size and bulk density, 1.8 g of nitric acid, 0.01 g of an organic acid (citric acid monohydrate) and 4 g of L-ascorbic acid are blended in the second aqueous solution, and nitric acid is added in an amount of 0. 3 g and 0.6 g of an amine compound (diethanolamine) were blended in the first aqueous solution, and the reaction temperature was 35 ° C., and flaky silver powder (a1-4, average particle size: 5.0 μm, average thickness: 0.08 μm, Bulk density: 2.3 g / cm ³ ) was obtained. Otherwise, a conductive paste was produced and evaluated in the same manner as in Example 1.
In Example 8, 2 g of nitric acid, 0.01 g of organic acid (citric acid monohydrate) and 4 g of L-ascorbic acid were blended only in the second aqueous solution, and ammonia water (a product with a concentration of 28% by weight) was added. 06 g was blended only in the first aqueous solution, the reaction temperature was 20 ° C., and flaky silver powder (a1-5, average particle size: 6.9 μm, average thickness: 0.08 μm, bulk density: 1.3 g / cm ^A conductive paste was produced and evaluated in the same manner as in Example 1 except that ³ ) was obtained.
The evaluation results obtained are shown in Table 2.

[Examples 9 to 10]
In Examples 9 to 10, as shown in Table 2, the type of binder resin in the conductive paste was changed from R1 of Example 1 to R2 (Example 9) and R3 (Example 10) below, respectively. Produced a conductive paste in the same manner as in Example 1 and measured the shielding characteristics and the like in the same manner. The evaluation results obtained are shown in Table 2.
(R2)
Epoxy resin: EPICLON830-S 17.5g
Reactive diluent: 5.0 g of butylphenyl glycidyl ether
Curing agent: 2.5g of 2P4MHZ-PW
Polyester resin solution (BC1): 20.0 g
Solvent (c1): 3.0 g
(R3)
Epoxy resin: EPICLON830-S 17.5g
Reactive diluent: 5.0 g of butylphenyl glycidyl ether
Curing agent: 2.5g of 2P4MHZ-PW
Urethane acrylic resin solution (BC2): 20.0g
Solvent (c1): 3.0 g

As described above, according to the present invention, as a silver powder, a predetermined flaky silver powder and a predetermined non-flaky silver powder are used in combination, and further processed into a film by further including a binder resin and a solvent. In addition to forming a silver powder laminated structure in which non-flaky silver powder enters into gaps such as the vertical direction of horizontally oriented flaky silver powder, and further along the surface of a three-dimensional electronic substrate, Since it followed well, even if the total compounding quantity of these silver powder was a comparatively small quantity (for example, 50 weight% or less of the whole quantity), a favorable shield characteristic came to be acquired.
Then, the production conditions of the flaky silver powder were adjusted, and the edges of the flaky silver powder were deformed by providing notches and making a jagged shape, or by providing a plurality of minute protrusions on the surface of the flaky silver powder. By using flaky silver powder, the value of the bulk density can be extremely lowered.
Therefore, the conductive paste of the present invention and the electromagnetic wave shielding member using such a conductive paste are suitable for use in conductive adhesives such as various electric products, electronic parts, and automobile products, and for grounding and shielding applications, respectively. Expected to be used for

10: Electronic equipment, 18: Conductive layer, 20: Electronic substrate, 22: Electronic element

Claims (8)

(A) A conductive paste that includes silver powder, (B) a binder resin, and (C) a solvent, forms a conductive layer on an electronic substrate on which an electronic element is mounted, and exhibits predetermined shielding characteristics Because
Said (A) silver powder is
(A1) When viewed in plan, the average particle diameter as the equivalent circle diameter is a value in the range of 5 to 30 μm, and the flaky silver powder has a thickness in the range of 0.01 to 2 μm;
(A2) a non-flaky silver powder having an average particle size of 1 to 5 μm and a bulk density of 0.3 to ³ g / cm ³ .
Furthermore, the blending amount of the (A) silver powder is set to a value within the range of 40 to 240 parts by weight with respect to 100 parts by weight of the (B) binder resin,
In addition, when the conductive layer is formed, a silver powder laminated structure in which the (a2) non-flaky silver powder enters into the gaps in the vertical direction of the plurality of (a1) flaky silver powders that are horizontally oriented is formed. A conductive paste characterized by   2. The conductive paste according to claim 1, wherein the shape of the (a1) flaky silver powder in a plan view is a circle or an ellipse.   The conductive paste according to claim 1 or 2, wherein the (a2) non-flaky silver powder is a chestnut-shaped silver powder and a spherical silver powder, or one of them.   The blending ratio (weight ratio) of the (a1) flaky silver powder and the (a2) non-flaky silver powder is set to a value within the range of 80:20 to 40:60. 4. The conductive paste according to any one of 3 above.   The conductive paste according to any one of claims 1 to 4, wherein the binder resin (B) is at least one of an epoxy resin, a polyester resin, and a urethane acrylic resin.   The solubility parameter (SP value) of the solvent (C) is set to a value in the range of 8.0 to 11.0, and the boiling point is set to a value in the range of 70 to 180 ° C. The electrically conductive paste as described in any one of -5.   7. The conductivity according to claim 1, wherein a specific resistance of a cured product of the conductive paste (amount of silver powder: 60 wt%) is set to a value of 1 × 10 Ohm · cm or less. Sex paste.   An electromagnetic wave shielding member comprising the conductive paste according to any one of claims 1 to 7 in a film form.