JPH11256208A - Copper fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide copper fine powder satisfying all characteristics required for the copper fine powder suitable for solventless type thermosetting electrically conductive paste for a via hole. SOLUTION: This copper fine powder for solventless type thermosetting electrically conductive paste for a beer hall is the one in which the electric resistance measured in a powder state is made to less than 1×10-<3> Ω.cm, the specific surface area by BET is made to 0.15 to 0.3 m<2> /g, the tap density is made to >=4.5 g/cc, the product of the grain size (μm) calculated from the specific surface are (m<2> /g) by BET in accordance with formula of the grain size (μm) = 6/[8.93×[the specific surface area (m<2> /g)] by BET] is made to >=13, the size distribution is made to D50 =4 to 7 μm and D90 =9 to 11 μm in microtrack measurement and the hydrogen reduction loss is made to <=0.30%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper fine powder having a remarkably low electric resistance in a powder state, an excellent filling property, and a sharp particle size distribution, and more particularly to a fine copper powder for an electronic circuit. More particularly, the present invention relates to a copper fine powder for a solventless thermosetting conductive paste suitable for filling a via hole (hereinafter referred to as VH) in a resin substrate for a multilayer printed wiring board.

[0002]

2. Description of the Related Art Conventionally, copper fine powder is applied to a substrate such as glass or ceramic for electronic equipment by screen printing or direct drawing, and then fired to form a thick film. Used as a raw material. These days,
In such electronic device circuit boards, further densification is required in accordance with the miniaturization and weight reduction of the device, the high speed for high performance, and the digitization. However, the conventional method of manufacturing a circuit board forms a through hole in the board by drilling,
A through-hole method for plating is mainly used, and there is a limit in satisfying the above requirements.

As a means for meeting such demands, attention has been paid to the development of a multilayer printed wiring board having a VH structure capable of responding to automatic wiring design and digital high-speed signal processing, in addition to miniaturization of a substrate size. A multi-layer printed wiring board with a VH structure is prepared by filling a hole in a drilled board with a non-solvent type thermosetting conductive paste composed of a fine copper powder, a resin and a curing agent, sandwiching a copper foil, and molding by heating and pressing. Manufacturing. In the thermosetting conductive paste used for manufacturing the substrate, unlike the conventional firing type paste, there is no volatilization of an organic binder or a solvent by heating and a non-conductive resin is interposed, so that copper as a conductor is used. The fine powder is required to have further excellent properties in conductivity and filling properties.

However, various attempts have heretofore been made to improve the properties of copper fine powder suitable for use in a sintering paste containing a solvent, ie, the shape, particle size, particle size distribution, tap density, etc. of the copper fine powder. However, the characteristics suitable for use in the solventless thermosetting conductive paste have not been sufficiently studied, and are suitable for use in the solventless thermosetting conductive paste for VH filling. Copper fine powder satisfying the characteristics has not yet been obtained.

Conventionally, mechanical pulverization, atomization, electrolysis, evaporation, and wet reduction have been proposed as methods for producing fine copper powder. The wet reduction method is considered to be a preferred method for producing fine copper powder for a firing paste, and the hydrazine reduction method of the wet reduction method is 0.1 to 10%.
Several methods have been proposed as means suitable for producing copper fine powder of the order of 0 μm.

A typical example is disclosed in Japanese Patent Application Laid-Open No. 2-29441.
No. 4, JP-A-4-116109, JP-A-4-116109
Production method described in JP-A-235205 and the like. JP-A-2-294414 discloses that an aqueous solution of a copper salt is treated with an alkali hydroxide in the presence of at least one compound selected from the group consisting of amino acids and salts thereof, ammonia and ammonium salts, organic amines and dimethylglyoxime. And a method of adding a reducing sugar to precipitate cuprous oxide, and then reducing with hydrazine to obtain a copper powder.

Further, Japanese Patent Application Laid-Open No. 4-116109 discloses that
A method of reducing an aqueous copper salt solution to metallic copper via copper hydroxide and cuprous oxide is disclosed. In the disclosed method, a reducing salt and a hydrazine-based reducing agent are added to the copper salt aqueous solution after adjusting the pH of the copper salt aqueous solution to 12 or more, and the reaction solution is adjusted to 60 ° C. or more before adding the hydrazine-based reducing agent. It also discloses that a complexing agent such as Rochelle salt, amino acid, ammonia or an ammonia compound can be used to stably dissolve copper (II) ions in an aqueous solution.

Further, Japanese Patent Application Laid-Open No. Hei 4-235205 discloses a reduction method similar to the reduction method described in Japanese Patent Application Laid-Open No. Hei 4-116109, which further comprises adding a protective colloid in portions. ing. The copper fine powder obtained by the production method disclosed in each of the above publications is characterized by a narrow particle size distribution and a small particle size, but the width of the particle size distribution is still wide and the particle size is small. However, it was still insufficient as a raw material for a non-solvent type thermosetting conductive paste for VH filling due to variation in the smaller one.

[0009]

In a resin substrate for a multilayer printed wiring board having a VH structure, unlike the case where a conventional sintering paste is used, a VH portion is provided between particles of copper fine powder as a conductor. The presence of the cured resin causes an increase in electric resistance. In addition, when filling the VH with the thermosetting conductive paste, a filling method using a squeegee or the like is performed. However, when there is a large variation in the particle size of the copper fine powder in the thermosetting conductive paste, the coarse particles are first placed. The proportion of fine particles in the thermosetting conductive paste filled in the VH and stored in the squeegee tends to increase as a result, and therefore, the number of substrates processed by one batch of the thermosetting conductive paste stored in the squeegee As the viscosity increases, the viscosity of the thermosetting conductive paste remaining on the squeegee gradually increases,
Eventually, inability to fill, poor filling, and adhesion of the paste remaining in portions other than the VH portion will occur.

In order to suppress the above inconveniences,
The following characteristics are required for the copper fine powder used for the thermosetting conductive paste. (1) electric resistance measured in a powder state is sufficiently low;
(2) It is excellent in the filling property for securing the conductivity, (3) The content of the copper fine powder in the thermosetting conductive paste can be increased, and (4) The paste while satisfying the above item (3). That the viscosity of is maintained moderately.

The present invention has been made in order to satisfy the above-mentioned requirements required for the copper fine powder used in the thermosetting conductive paste, and an object of the present invention is to satisfy all the above characteristics. To provide a copper fine powder for a solventless thermosetting conductive paste for via holes.

[0012]

Means for Achieving the Object The present inventors have conducted various studies to achieve the above object, and as a result, the electrical resistance measured in a powder state, the specific surface area by BET, the tap density, the specificity by BET. The product of the particle diameter and tap density calculated from the surface area, the value of the particle size distribution and hydrogen reduction loss in microtrack measurement satisfying all of the above characteristics that the copper fine powder is within a specific range, furthermore, The present inventors have found that a copper fine powder satisfying all the above characteristics can be obtained by a specific production method, and completed the present invention.

That is, the copper fine powder of the present invention has an electric resistance of 1 × 10 ⁻³ Ω · cm or less measured in a powder state,
The specific surface area by T is 0.15 to 0.3 m ² / g,
The tap density is 4.5 g / cc or more, and from the specific surface area (m ² / g) by the BET, the particle size (μm) = 6 / [8.93 × [specific surface area by BET (m ² / g)] ] And the tap density (g / c) calculated according to
c) is 13 or more, and the particle size distribution is D ₅₀ = 4 to 7 μm and D ₉₀ = 9 to 11 in microtrack measurement.
It is a solvent-free thermosetting conductive paste fine copper powder for via holes, wherein the fine powder has a reduction in hydrogen reduction of 0.30% or less.

The copper fine powder of the present invention is prepared by adding a reaction equivalent or more of an alkali hydroxide to an aqueous copper salt solution of divalent copper ion maintained at a temperature of 55 ° C. or more to form cupric oxide. While maintaining the above temperature, reducing sugar is gradually added to reduce the cupric oxide to cuprous oxide, and then filtered and washed, and reslurried, and the pH is adjusted to 5.5 to 8.5. It can be produced by gradually adding a hydrazine-based reducing agent in the presence of a maintained pH buffer to reduce the cuprous oxide to metallic copper.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The copper fine powder of the present invention has an electric resistance of 1 × 10 ⁻³ Ω · cm or less measured in a powder state. When the electric resistance exceeds 1 × 10 ⁻³ Ω · cm, when a resin substrate for a multilayer printed wiring board having a VH structure is formed by a thermosetting conductive paste using the copper fine powder, the electric resistance of the VH portion is reduced. It is not preferable because it becomes high.

The fine copper powder of the present invention has a specific surface area by BET of 0.15 to 0.3 m ² / g. This BET
When the specific surface area is less than 0.15 m ² / g, a resin substrate for a multilayer printed wiring board having a VH structure is formed using a thermosetting conductive paste using the copper fine powder.
The viscosity of the paste filled therein is too low, so that a cavity is formed in the central portion of the filled paste, and a phenomenon in which the paste in the hollow portion is turret downward occurs, which is not preferable. Conversely, BE
When the specific surface area by T exceeds 0.3 m ² / g,
Since the particle size of the copper fine powder is small and agglomeration proceeds, the viscosity of the paste increases, and as the viscosity of the paste increases, it becomes increasingly difficult to fill the hole of the substrate with the thermosetting conductive paste, and the substrate manufacturing capacity ( Productivity) is not preferred.

The fine copper powder of the present invention has a tap density of 4.5 g.
/ Cc or more. This tap density is 4.5 g /
In the case of less than cc, when a resin substrate for a multilayer printed wiring board having a VH structure is formed with a solventless thermosetting conductive paste using the copper fine powder, the filling rate of the copper fine powder into the VH becomes insufficient. As a result, the electric resistance of the VH portion increases, which is not preferable.

The copper fine powder of the present invention has a particle size (μm) = 6 / [8.93 × [specific surface area according to BET (m ² / g)] from the above specific surface area (m ² / g) according to BET. ] And the tap density (g / c) calculated according to
The product with c) is 13 or more. When the product of the particle size and the tap density is less than 13, for example, when the tap density is sufficiently high but the particle size of the copper fine powder is too small, the viscosity of the solventless thermosetting conductive paste is Is higher,
As the viscosity of the paste increases, it becomes increasingly difficult to fill the holes of the substrate with the solvent-free thermosetting conductive paste, and the substrate manufacturing capacity (productivity) decreases.
If the tap density is too small even if the particle diameter is within a predetermined range, when a resin substrate for a multilayer printed wiring board having a VH structure is formed by a solventless thermosetting conductive paste using the copper fine powder, The filling rate of the copper fine powder into the VH becomes insufficient, and as a result, the electric resistance of the VH portion increases, which is not preferable.

The fine copper powder of the present invention has a particle size distribution of D ₅₀ = 4 to 7 μm and D ₉₀ = 9 to 10 in microtrack measurement.
11 μm. D ₅₀ is less than 4 μm or D ₉₀ is 9
In the case of less than μm, when a resin substrate for a multilayer printed wiring board having a VH structure is formed from a thermosetting conductive paste using the copper fine powder, the viscosity of the paste filled in the VH is too low. Since the viscosity is too low, a cavity is formed in the center of the filled paste, and the phenomenon that the paste in the cavity is turret downward occurs, which is not preferable. Conversely, D
_{When 50} exceeds 7 μm or D ₉₀ exceeds 11 μm, the agglomeration of the copper fine powder is too large to increase the viscosity of the paste, and as the viscosity of the paste increases, the solventless thermosetting conductive material flows into the holes of the substrate. It is not preferable because the filling of the conductive paste gradually becomes difficult, and the substrate manufacturing capability (productivity) is reduced.

In the method for producing a copper fine powder of the present invention,
First, a temperature of 55 ° C. or higher, preferably 60 to 70 ° C.
A cupric oxide is formed by adding an alkali hydroxide in an amount of at least a reaction equivalent, preferably 1 to 2 times the reaction equivalent, to an aqueous solution of a copper salt of divalent copper ion maintained at a temperature of ° C. Examples of the copper salt of divalent copper ion used here include copper sulfate, copper chloride, copper nitrate, and copper acetate.

This step of producing cupric oxide is indispensable for promoting the subsequent reduction with a reducing sugar.
When the temperature of the aqueous copper salt solution is lower than 55 ° C. or the alkali hydroxide has a reaction equivalent less than the equivalent of divalent copper ions, the shape and particle size distribution of the copper fine powder finally formed may be reduced. This is not preferred because it not only causes variations but also affects the progress of the reaction. Although each of the above publications discloses that copper hydroxide is generated by an alkali hydroxide or the like, the point that divalent copper ions are completely converted to cupric oxide using excess alkali is described. No mention or suggestion is made.

While maintaining the cupric oxide produced as described above at a temperature of 55 ° C. or higher, preferably at a temperature of 60 to 70 ° C., a reducing sugar is gradually added to reduce the cupric oxide. Reduce to one copper. At this time, if the temperature is lower than 55 ° C. or the reducing sugar is added at once, that is, if the reducing sugar is not added gradually, the shape and the particle size distribution of the finally formed copper fine powder are also varied. Absent.

The cuprous oxide slurry produced as described above is then filtered, washed, and reslurried in a neutral range, and then the pH is adjusted to 5.5 to 8.5, preferably 6 to 7.5. The cuprous oxide is reduced to metallic copper by gradually adding a hydrazine-based reducing agent in the presence of an appropriate pH buffer to be maintained.
The pH buffer used here is aminoacetic acid, and the hydrazine-based reducing agents include hydrazine, hydrated hydrazine, hydrazine sulfate, hydrazine carbonate, hydrazine hydrochloride and the like.

The above publications disclose that various additives are added to the first aqueous solution of copper salt in order to stabilize the divalent copper ions in the solution. Reduction treatment of copper oxide slurry is in progress. As described above, on the alkali side, a large amount of nuclei for copper fine powder generation is generated due to the strong reducing power of the hydrazine-based reducing agent, and the obtained copper fine powder is relatively small with respect to the target particle size,
The particle size also varies, and a lot of agglomerates are generated, so that the viscosity of the thermosetting conductive paste using the copper fine powder is increased, and the filling rate into VH is deteriorated. I can't get it.

[0025] The present inventors, in order to suppress such adverse effects,
Prior to the reduction with the hydrazine-based reducing agent, the cuprous oxide slurry was filtered and washed, reslurried in a neutral region, and a method of adding a pH buffer at the time of the reduction was found. In the method for producing a copper fine powder of the present invention, it is important to filter, wash, and re-slurry the cuprous oxide slurry. When such treatment is not performed, the finally obtained fine copper powder has an electric resistance of 1 × 10 ⁻³ Ω measured in a powder state.
・ Cm or specific surface area by BET is 0.3m ²
/ Or more than g, or the product of the particle size and tap density calculated from the specific surface area by BET is less than 13, or a particle size distribution D ₅₀ in the micro-track measurement is less than 4,
D ₉₀ is less than 9, or the hydrogen reduction weight loss is 0.3
It exceeds 0%.

In the method for producing copper fine powder of the present invention, when reducing cuprous oxide to metallic copper, a pH buffer such as aminoacetic acid having an isoelectric point of about pH 6 is used to reduce the pH buffer. Is involved in the catalytic reaction to stabilize the concentration of the hydrazine-based reducing agent in the slurry, or the pH buffer is considered to form a condensate with the hydrazine-based reducing agent. The concentration of the hydrazine-based reducing agent in the slurry to be produced can be kept almost constant.

In the method for producing a copper fine powder of the present invention,
Use a suitable pH buffer to maintain the pH between 5.5 and 8.5. If the pH range maintained by the pH buffer is less than 5.5 or greater than 8.5, the above effect cannot be obtained. The pH buffer addition rate is 0.01 to 1
Mole / copper mole, preferably 0.05 to 0.4 mole.
A mole / copper mole is good. pH buffer addition rate is 0.0
If it is less than 1 mol / mol of copper, the effect of the pH buffer is small. If it exceeds 1 mol / mol of copper, the individual particles grow too large, and the solvent-free type using the copper fine powder is used. The content of fine copper powder in the thermosetting conductive paste tends to be low. Further, the reaction temperature is preferably about 40 to 60 ° C. If the temperature is lower than 40 ° C., the reduction rate becomes slow,
If the temperature exceeds the above, an effect corresponding to the cost required for heating cannot be obtained.

In the method for producing fine copper powder of the present invention,
If the hydrazine-based reducing agent is added all at once, that is, if the hydrazine-based reducing agent is not added gradually, the shape and the particle size distribution of the finally formed copper fine powder are undesirably varied. Further, gum arabic, gelatin or the like may be added as a protective colloid when reslurrying. Furthermore, by treating the copper fine powder after reduction and filtration with a suitable fatty acid in such an amount that a monomolecular film is formed on the surface of the copper fine powder, stability with time against oxidation can be imparted.

The copper fine powder obtained as described above has an electric resistance measured in a powder state of 1 × 10 ⁻³ Ω · cm or less and a specific surface area by BET of 0.15 to 0.3 m ² / cm.
g, and has a tap density of 4.5 g / cc or more, the ratio by said BET surface area (m ² / g) from the formula particle size (μm) = 6 / [8.93 × [specific surface area by BET (m ² / g)]] and the tap density (g / c)
c) is 13 or more, and the particle size distribution is D ₅₀ = 4 to 7 μm and D ₉₀ = 9 to 11 in microtrack measurement.
μm and a copper fine powder having a hydrogen reduction loss of 0.30% or less.

[0030]

The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to such examples. Example 1 100 kg of copper sulfate (pentahydrate) was dissolved in warm water to prepare a 200 liter aqueous solution, which was maintained at 60 ° C. To this aqueous solution was added 125 liters of 25% by weight of sodium hydroxide, and the mixture was stirred for 1 hour while maintaining the temperature at 60 ° C., and reacted to produce cupric oxide.

While maintaining the above reaction product at 60 ° C., 80 l of a glucose solution having a concentration of 450 g / l was quantitatively added thereto over 1 hour to form a cuprous oxide slurry. This slurry was filtered and washed, and re-slurried by adding hot water to make a 320-liter slurry, to which 1.5 kg of aminoacetic acid and 0.7 g of gum arabic were added.
kg was added, stirred and the temperature was maintained at 50 ° C. To this slurry, 50 liters of 20% hydrazine hydrate was quantitatively added over 1 hour to produce a copper fine powder. The obtained copper fine powder slurry was filtered, sufficiently washed with pure water, and filtered, and then the obtained copper fine powder was subjected to 25 g of oleic acid.
And then immersed in methanol containing for 30 minutes, followed by ordinary drying and sieving to obtain fine copper powder. FIG. 1 shows a microphotograph (approximately 10,000 times) of this fine copper powder. As is clear from FIG. 1, the obtained copper fine powder has a polyhedral shape.

Examples 2 to 4 In the production method described in Example 1, the amount of aminoacetic acid added was changed from 1.5 kg to 3 kg, 15 kg and 30 kg, respectively.
Except having changed to, the copper fine powder was obtained by the same manufacturing method as in Example 1. The copper fine powder obtained in Examples 1 to 4 had a polyhedral shape similarly to the copper fine powder obtained in Example 1.

Comparative Example 1 A copper fine powder was obtained in the same manner as in Example 1 except that no aminoacetic acid was added. Comparative Example 2 Copper fine powder was obtained by the same production method as in Example 1 except that 3 kg of aminoacetic acid was added to the aqueous copper sulfate solution before the start of the reaction. Comparative Example 3 A copper fine powder was obtained by the same production method as in Example 1, except that filtration washing was not performed after the formation of the cuprous oxide slurry.

Evaluation of Characteristics The characteristics of the copper fine powder and the characteristics of the resin substrate for a multilayer printed wiring board having a VH structure formed using a thermosetting conductive paste containing the copper fine powder were evaluated. The copper fine powders to be evaluated were the copper fine powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3, respectively, a commercially available METZ product # 12 (Comparative Example 4), ME
TZ product # 13 (Comparative example 5), Nippon Atomize copper powder (Comparative example 6), and Kyoto Elex product C-200
The properties of the copper fine powder evaluated in 11 types of (Comparative Example 7) were the electrical resistance measured in the powder state, the specific surface area by BET, the tap density, and the particle size (μm) calculated from the specific surface area by BET. The product with the tap density (g / cc), the particle size distributions D ₅₀ and D ₉₀ in Microtrack measurement, and the hydrogen reduction weight loss were obtained. The values were as shown in Table 1 below.

In evaluating the characteristics of a resin substrate for a multilayer printed wiring board having a VH structure formed using a thermosetting conductive paste containing copper fine powder, first, 85% by weight of copper fine powder and the resin composition 3% by weight of bisphenol A type epoxy resin (Epicoat 828, manufactured by Yuka Shell Epoxy), 9% by weight of epoxy resin obtained by glycidyl esterification of dimer acid (YD-171, manufactured by Toto Kasei), and amine duct curing as a curing agent 3 wt% of an agent (MY-24, manufactured by Ajinomoto) was kneaded with a three-roll mill to prepare a thermosetting conductive paste.

On the other hand, using a drill, an aramid epoxy sheet (R1) having a thickness of 200 μm and a size of 10 cm × 10 cm was used.
661, manufactured by Matsushita Electric Works), a through hole having a diameter of 0.2 mm, a distance between the center axes of the through holes of 3 mm, and a 20 × 2 through hole in a lattice shape.
5 = 500 were formed to obtain a substrate having a VH structure. A stainless steel squeegee was placed at an angle of 45 ° with respect to this substrate, and 10 g of the paste prepared above was used.
00 sheets were continuously supplied, and the through holes of each substrate were filled with the paste.

The thermosetting conductive paste containing the copper fine powder of each of the examples and comparative examples was used to prepare 2
With respect to the 0, 40, 60, 80, and 100th resin substrates for a multilayer printed wiring board having a VH structure, the appearance of filling in VH and the remaining state of the copper fine powder component on the substrate were visually evaluated according to the following criteria. Filling appearance ：: A state in which all VHs are completely filled visually, Δ: A state in which all the VHs are filled visually but VH which is not completely filled is within 5%, ×: The above State other than ○ and △. Residual state of copper fine powder component on substrate ○: State where no paste component remains on substrate after filling △: State where lightly stains when touching finger on substrate after filling ×: Filling Thereafter, a state in which the paste component remains on the substrate can be visually observed.

Further, 20, 40,
A copper foil of 18 μm is placed on the upper and lower surfaces of the 60th, 80th and 100th substrates at a pressing temperature of 180 ° C. and a pressure of 50 kg / cm ² for 60 hours.
Heating and pressurizing for minutes, a double-sided copper clad board was prepared. Next, an electrode pattern was formed using a known etching technique, and the connection resistance value (via resistance) of the inner via hole was measured. The results were as shown in Tables 2 and 3.
As is clear from the data shown in Tables 2 and 3, as compared with the substrate manufactured using the copper fine powder of the comparative example, the substrate manufactured using the copper fine powder of the example was excellent in the filling property and the substrate was manufactured. It can be seen that there is no residual fine copper powder and the via resistance is sufficiently low.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

The copper fine powder of the present invention sufficiently satisfies the characteristics required for the raw materials used for the solventless thermosetting conductive paste. That is, in a resin substrate for a multilayer printed wiring board having a VH structure, the copper fine powder of the present invention exhibits excellent filling properties since it has a high tap density and a narrow particle size distribution. In addition to the excellent filling properties, the fine copper powder has a polyhedral shape, so that the degree of contact between the particles is high and the electric resistance is stably low. Furthermore, even when the VH is filled with a thermosetting conductive paste using a squeegee, the viscosity of the paste stored in the squeegee does not change much even if the number of substrates to be continuously processed increases, and the paste is applied to the substrate. The adhesion is slight, and the number of processed substrates per processing is dramatically improved as compared with the case where the conventional copper fine powder is used. Therefore, it is possible to dramatically improve the performance and productivity of the resin substrate for a multilayer printed wiring board having a VH structure.

[Brief description of the drawings]

FIG. 1 is a micrograph of the copper fine powder obtained in Example 1.

Claims (1)

[Claims] An electric resistance measured in a powder state is 1 × 10 ^−3.
Ω · cm or less and specific surface area by BET is 0.15
０．３0.3 m ² / g and tap density 4.5 g / cc
The particle size (μm) calculated from the BET specific surface area (m ² / g) according to the formula: Particle size (μm) = 6 / [8.93 × [BET specific surface area (m ² / g)]] ) And tap density (g / c)
c) is 13 or more, and the particle size distribution is D ₅₀ = 4 to 7 μm and D ₉₀ = 9 to 11 in microtrack measurement.
A copper fine powder for a solvent-free thermosetting conductive paste for via holes, characterized in that the copper fine powder has a thickness of 0.3 μm and a hydrogen reduction loss of 0.30% or less.