CN119255877A

CN119255877A - Copper powder

Info

Publication number: CN119255877A
Application number: CN202280096144.4A
Authority: CN
Inventors: 土桥礼奈; 折笠广典
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2022-07-08
Filing date: 2022-07-29
Publication date: 2025-01-03
Also published as: KR20240167686A; JP2024008681A; TW202402678A; WO2024009522A1

Abstract

A copper powder, wherein the ratio (C/SSA) of the carbon content C (mass%) to the BET specific surface area (m ²/g) is 0.07 or less, and the peak area ratio (A2/A1) of the area A2 of the peak having the peak top in the range of 284eV to 289.2eV to the area A1 of the peak having the peak top in the range of 284eV to 284eV in the C1s spectrum obtained by X-ray photoelectron spectroscopy is 0.5 or more.

Description

Copper powder

Technical Field

The present specification discloses a technique related to copper powder.

Background

Among conductive pastes containing copper powder and used for forming circuits on a substrate by printing, bonding a semiconductor element to a substrate, and the like, there is a sintered conductive paste in which copper powder contained in the paste is sintered by heating at the time of use.

Sintering type conductive pastes require copper powder to be sintered with relatively low temperature heating. This is because, when the temperature at the time of heating is high, the heat may affect the substrate and the semiconductor element. In addition, when heating at a high temperature and when cooling after heating, a large thermal stress is generated in the substrate or the semiconductor element, which may also change the electrical characteristics of the circuit or the semiconductor element.

Patent document 1 proposes "a copper powder having an average particle diameter of 0.05 to 2 μm as observed by SEM, in which the BET specific surface area value (SSA) (m ²/g) and the carbon content (C) (wt%) of the copper powder are in the relationship of the following formula [1], as a technical problem of providing a copper powder and a copper paste for coating a copper-containing powder capable of electroless metal plating without using a high-priced catalyst such as palladium in the production of a conductive coating film, and a method for producing a conductive coating film efficiently by electroless metal plating a copper-containing powder coating film formed using the copper paste". C/SSA is less than or equal to 7 x 10 ^－2.

Prior art literature

Patent literature

Patent document 1 International publication No. 2012/157704

Disclosure of Invention

Problems to be solved by the invention

Although various studies and developments have been made on low-temperature sintering of copper powder, sintering at a still lower temperature is sometimes required.

In the present specification, copper powder having excellent low-temperature sinterability is disclosed.

Solution for solving the problem

The copper powder disclosed in the present specification has a ratio (C/SSA) of a carbon content C (mass%) to a BET specific surface area (m ²/g) of 0.07 or less, and a peak area ratio (A2/A1) of an area A2 having peaks in a range of 284ev to 289.2ev to an area A1 having peaks in a range of 284ev to 284ev in a C1s spectrum obtained by X-ray photoelectron spectroscopy of 0.5 or more.

Effects of the invention

The copper powder has excellent low-temperature sinterability.

Drawings

FIG. 1 is a C1s spectrum obtained by XPS in invention example 5.

Detailed Description

Hereinafter, embodiments of the copper powder will be described in detail.

In the copper powder according to one embodiment, the ratio (C/SSA) of the carbon content C (mass%) to the BET specific surface area (m ²/g) is 0.07 or less, and the peak area ratio (A2/A1) of the area A2 of the peak having the peak top in the range of 284ev to 289.2ev to the area A1 of the peak having the peak top in the range of 284ev to 284ev in the C1s spectrum obtained by X-ray photoelectron spectroscopy is 0.5 or more.

Details of such copper powder will be described later, and the ratio (C/SSA) of the carbon content C (mass%) to the BET specific surface area (m ²/g) is small, whereby sintering is easy at a relatively low temperature. In the copper powder, a predetermined peak area ratio (A2/A1) in the C1s spectrum obtained by XPS is larger. Here, the peak having the peak top in the range of 284ev to 284ev corresponds to carbon bonded to a carbon atom, and the peak having the peak top in the range of 284ev to 289.2ev higher than the energy side corresponds to carbon forming a double bond with oxygen. Copper powder having a peak area ratio (A2/A1) of these values is considered to contain an organic substance having a high oxygen content. When the organic matter having a high oxygen content is heated to several hundred degrees or more, CO and CO ₂ are easily generated by thermal decomposition, and solid carbon is not easily left as a thermal decomposition residue. Therefore, it is considered that copper powder coated with an organic substance having a high oxygen content is easily sintered at a relatively low temperature. However, not limited to such a theory.

(BET specific surface area)

The BET specific surface area of the copper powder is preferably 0.5m ²/g or more and 10.0m ²/g or less. When the BET specific surface area is more than 10.0m ²/g, it is difficult to secure oxidation resistance, and problems may occur in paste properties due to moisture absorption, aggregation, and the like. On the other hand, when the BET specific surface area is too small, the copper powder may have a large particle size and may not be sintered at a low temperature, and the smoothness of the circuit or the junction surface on which the paste is printed may be insufficient. From this viewpoint, the BET specific surface area of the copper powder is preferably 0.5m ²/g～10.0m²/g, and more preferably 2.0m ²/g～6.0m²/g.

The BET specific surface area of copper powder can be measured by, for example, deaerating copper powder in vacuum at 70℃for 5 hours in accordance with JIS Z8830:2013, and then using BELSORP-mini II from MicrotracBEL.

(Average particle diameter)

The average particle diameter of the copper powder is preferably 0.05 μm to 2.00. Mu.m, more preferably 0.05 μm to 1.50. Mu.m, particularly preferably 0.1 μm to 0.5. Mu.m. If the average particle size of the copper powder is too large, the copper powder may not be sintered at a low temperature, and the smoothness of a circuit or a junction surface on which the paste is printed may be insufficient. Further, if the average particle diameter of the copper powder is too small, it is difficult to secure oxidation resistance, and there is a possibility that problems may occur in paste properties due to moisture absorption, aggregation, or the like.

The average particle diameter of the copper powder can be calculated from the value of the BET specific surface area using the following formula.

D=6/(ρ×SSA)

Here, D is the average particle diameter, ρ is the true density of copper, and SSA is the BET specific surface area.

(C/SSA)

Copper powder generally contains carbon because organic reducing agents and dispersing agents are used in the production process. When the BET specific surface area (m ²/g) of the copper powder is "SSA" and the carbon content (mass%) of the copper powder is "C", the ratio (C/SSA) of the copper powder according to the embodiment is 0.07 or less. When the ratio (C/SSA) is more than 0.07, the carbon content is too large relative to the BET specific surface area, and thus excellent preservability and dispersibility can be obtained, but carbon remains on the surface of the copper powder as a thermal decomposition residue of the organic reducing agent and the dispersant in the sintering process, and sintering of the copper powder is not easily performed. Namely, the low-temperature sinterability is impaired. Therefore, the above ratio is 0.07 or less, more preferably 0.05 or less.

On the other hand, if the ratio (C/SSA) of the carbon content C (mass%) to the BET specific surface area (m ²/g) is small, there is a possibility that the oxidation resistance is impaired or the compatibility with an organic solvent is poor, and the paste having excellent dispersibility is not obtained. Therefore, the ratio (C/SSA) is preferably 0.01 or more, more preferably 0.02 or more.

The carbon content of the copper powder (C/SSA) used to calculate the ratio of the carbon content C (mass%) to the BET specific surface area (m ²/g) was measured by the high-frequency induction furnace combustion-infrared absorption method. Specifically, the carbon content of the copper powder can be measured using a carbon-sulfur analyzer such as CS844 made of LECO, LECOCEL II made of LECO, a Fe sheet, and the like as the combustion improver, and a fiber measurement (step pin) as a calibration curve.

(O/SSA)

In order to eliminate the organic matter contained in the copper powder as CO or CO ₂ by thermal decomposition in the sintering process, oxygen needs to be contained in the copper powder. When the BET specific surface area (m ²/g) of the copper powder is "SSA" and the oxygen content (mass%) of the copper powder is "O", the ratio (O/SSA) of the copper powder according to the embodiment is greater than 0.15. If the ratio (O/SSA) is greater than 0.15, the organic matter contained in the copper powder is easily converted into CO and CO ₂ in the sintering process, and the copper powder is excellent in low-temperature sinterability. The ratio (O/SSA) is preferably greater than 0.15, and more preferably 0.17 or more.

The ratio (O/SSA) of the oxygen content O (mass%) to the BET specific surface area (m ²/g) is preferably 0.5 or less, more preferably 0.3 or less. The reason for this is that an excessively large ratio (O/SSA) means that oxygen is not only derived from oxidation of an organic substance, but also that the surface of copper powder is significantly oxidized, and that the characteristics of the paste after adjustment using the present copper powder are affected by instability or the like.

The oxygen content of copper powder used in determining the ratio (O/SSA) of oxygen content O (mass%) to BET specific surface area (m ²/g) was measured by the inert gas melt-infrared absorption method. Here, LECO TC600 was used as an oxygen and nitrogen analyzer, a calibration curve was measured using a measuring fiber, and copper powder was put into a nickel capsule for measurement.

(XPS peak area ratio)

When copper powder was analyzed by X-ray photoelectron spectroscopy, a C1s spectrum was obtained as a spectrum of the 1s orbit of C as a result of the analysis. In the C1s spectrum, a peak area ratio (A2/A1) of a ratio of an area A2 of a peak having a peak top in a range of 284eV to 289.2eV to an area A1 of a peak having a peak top in a range of 284eV to 284eV is 0.5 or more.

Here, the peak of 284ev to 284ev corresponds to electrons in the 1s orbital of carbon that is not bonded to an atom having high polarity such as oxygen. Herein, it is identified as corresponding to carbon having a C-C bond. On the other hand, the peak at the high energy side of 288eV to 289.2eV corresponds to an electron in the 1s orbital of carbon bonded to an atom having high polarity such as oxygen, and is identified as corresponding to carbon having a C-O double bond. When the copper powder contains an organic substance having a large oxygen content, the peak intensity of the latter is relatively higher than that of the former, and the peak area ratio (A2/A1) is large. When the peak area ratio (A2/A1) is 0.5 or more, CO and CO ₂ are easily generated as thermal decomposition products of organic substances when the copper powder is heated, and carbon as a thermal decomposition residue is less likely to remain on the surface of the copper powder. Therefore, it is considered that sintering of copper powder is easily performed at a relatively low temperature. From such a viewpoint, the peak area ratio (A2/A1) is more preferably 0.6 or more. On the other hand, the peak area ratio (A2/A1) is usually not more than 10, and sometimes 1.0 or less.

In the C1s spectrum obtained by the X-ray photoelectron spectroscopy, the peak area ratio (A3/A1) which is the ratio of the area A3 of the peak having the peak top in the range of 284ev to the area A1 of the peak having the peak top in the range of 284ev to 284ev is preferably 0.3 or more.

The area of the peak having the peak top at the position of 288eV is regarded as the area A2.

The peak of 284 eV to 284 eV corresponds to a carbon atom forming a single bond with oxygen. Copper powder having a peak area ratio (A3/A1) of 0.3 or more is copper powder excellent in low-temperature sinterability, but the reason for this is not clear. The peak area ratio (A3/A1) is preferably 0.3 to 0.7, more preferably 0.3 to 0.5.

In order to determine the peak area ratio (A2/A1) and the peak area ratio (A3/A1), X-ray photoelectron spectroscopy (XPS) was measured and analyzed as follows.

Device PHI 5000Versa Probe II (with neutralization gun) manufactured by ULVAC-PHI Co., ltd.

Excitation source, monochromatization AlK alpha.

Output 25.0W.

Detection area 100 μm phi.

The incident angle is 90 degrees.

Glancing angle (sweep-off angle) 45 degrees.

In the measurement, copper powder was molded into a pellet and measured.

For analysis of the measured data, data analysis software, multiPak manufactured by ULVAC-PHI Co., ltd. In data analysis, peak segmentation was performed using the fogget function (Voigt function), and the area of each peak was calculated. The position of the peak with the lowest binding energy among the peaks attributable to C1s was corrected to 284.8eV.

(Low temperature sinterability)

In addition, the copper powder can be sintered at a relatively low temperature. The low-temperature sinterability can be confirmed as follows. About 0.3g of copper powder was charged into a cylindrical die having a diameter of 5mm, and then uniaxially pressed to prepare compressed powder particles having a cylindrical shape of about 3mm in height and a density of 4.7.+ -. 0.1 g/cc. Thereafter, the above-mentioned powder compact particles were heated at a rate of 10 ℃ per minute from 25 ℃ under an atmosphere containing 2% by volume of hydrogen (H ₂) and the balance being nitrogen (N ₂) using a thermo-mechanical analysis apparatus (TMA). At this time, as the temperature increases, the copper particles constituting the green compact particles sinter, the volume of the green compact decreases, and the density approaches that of metallic copper (about 8.9g/cm ³). When the rate of change in the columnar height of the powder particles in the shrinkage direction is referred to as a linear shrinkage rate, a copper powder having excellent low-temperature sinterability can be evaluated as a copper powder having a low temperature at a linear shrinkage rate of 5%. In particular, the temperature at which the linear shrinkage is 5% is preferably 350 ℃ or less.

(Manufacturing method)

The copper powder described above can be produced by, for example, using a chemical reduction method, a disproportionation method, or the like. The production of copper powder is not limited to this, and details of the chemical reduction method are as follows.

In the case of using the chemical reduction method, for example, a step of preparing an aqueous copper salt solution, an aqueous alkaline solution, an aqueous reducing agent solution, and the like as raw material solutions, a step of mixing and reacting these raw material solutions to obtain a slurry containing copper particles, a step of washing copper particles, a step of performing solid-liquid separation, a step of drying, and a step of pulverizing as needed are sequentially performed.

In a more specific example, after the aqueous copper sulfate solution is heated to an appropriate reaction temperature, the pH is adjusted with an aqueous sodium hydroxide solution or an aqueous ammonia solution, and then an aqueous hydrazine solution is added at once to react, thereby reducing copper sulfate to cuprous oxide particles having a particle diameter of about 100 nm. After the slurry containing the cuprous oxide particles was heated to the reaction temperature, an aqueous solution containing sodium hydroxide and hydrazine was added dropwise, and then an aqueous solution of hydrazine was added dropwise, whereby the cuprous oxide particles were reduced to copper particles. After the completion of the reaction, the obtained slurry was filtered, washed with pure water and methanol, and dried. Copper powder is thus obtained.

A reducing agent such as hydrazine added to the copper sulfate aqueous solution is used to reduce cupric oxide to cuprous oxide. In this case, if the reducing agent is added at one time, the cuprous oxide particles thus produced tend to be finer as described above. After the formation of finer cuprous oxide particles, the reducing agent may be added separately. After the formation of the cuprous oxide particles, the first addition of the reducing agent can be used mainly for the formation of the metallic copper nuclei, and the second addition of the reducing agent can be used for the growth of the metallic copper nuclei.

In the above production, an aqueous solution of copper sulfate or copper nitrate may be used as the aqueous solution of copper salt. The alkaline aqueous solution may be, for example, an aqueous solution of NaOH, KOH, NH ₄ OH, or the like. As the reducing agent of the aqueous reducing agent solution, besides hydrazine, organic substances such as sodium borohydride and glucose are mentioned.

Organic substances such as complexing agents and dispersants may be added as needed during the copper powder production process. For example, gelatin, ammonia, gum arabic, or the like may be added more than once between the step of preparing the raw material solution and the step of obtaining a slurry containing copper particles.

(Use)

The copper powder thus produced is mixed with, for example, a resin material, a dispersion medium, and the like to form a paste, and is particularly suitable for use in a conductive paste or the like that can be used for bonding a semiconductor element to a substrate or forming a wiring.

Examples

Next, the effect of the copper powder was confirmed by trial production, and therefore will be described below. However, the description herein is for the purpose of illustration only and is not intended to be limiting.

(Inventive example 1)

First, a slurry containing nanoparticles of cuprous oxide (average particle diameter: about 100 nm) was synthesized by mixing 2400g of copper sulfate pentahydrate and 30g of citric acid in 8.7L of pure water at a time with 6.7L of a mixed aqueous solution of 540g of sodium hydroxide and 144g of hydrazine monohydrate. Next, the slurry in which the cuprous oxide particles were suspended was heated to 50 ℃ or higher, and a mixed aqueous solution of 29g of hydrazine monohydrate and 252g of sodium hydroxide was added dropwise to 4.5L, followed by adding an aqueous solution of sodium hydroxide to adjust pH. Thereafter, 115g of hydrazine monohydrate 1.3L of an aqueous solution was further added dropwise to reduce cuprous oxide to metallic copper. After the completion of the reaction, the mixture was repeatedly decanted, washed with water, dried, and pulverized to obtain copper powder.

(Inventive example 2)

The procedure of invention example 1 was repeated until a slurry containing cuprous oxide was synthesized. Then, 4.5L of a mixed aqueous solution of 43g of hydrazine monohydrate and 252g of sodium hydroxide was added dropwise, the pH was adjusted, and 1.3L of an aqueous solution of 101g of hydrazine monohydrate was further added dropwise to reduce cuprous oxide to metallic copper, and the resultant was washed with water, dried and pulverized in the same manner.

Inventive examples 3, 4 and 5

The procedure of invention example 1 was repeated until a slurry containing cuprous oxide was synthesized. Then, a mixed aqueous solution of 72g of hydrazine monohydrate and 252g of sodium hydroxide was added dropwise to adjust the pH of the mixture to 4.5L, and further, an aqueous solution of 72g of hydrazine monohydrate was added dropwise to 1.3L to reduce cuprous oxide to metallic copper, followed by washing with water, drying, and pulverization in the same manner.

Comparative example 1

To an aqueous solution obtained by dissolving 2400g of copper sulfate pentahydrate and 30g of citric acid in 8.7L of pure water, 6.7L of a mixed aqueous solution of 540g of sodium hydroxide and 144g of hydrazine monohydrate was added dropwise to synthesize cuprous oxide. Next, the slurry in which cuprous oxide was suspended was adjusted to 70 ℃, and an aqueous sodium hydroxide solution was added to adjust the pH to 10. Thereafter, 14g of hydrazine monohydrate and sodium hydroxide were added to start reducing a portion of the cuprous oxide to metallic copper. After further addition of aqueous citric acid solution, hydrazine monohydrate was added and the reduction was smoothly performed for several hours. After the reaction, washing, drying and crushing are carried out to obtain copper powder. To 600g of this copper powder, 2L of an aqueous solution containing 0.3g of malonic acid having a high oxygen concentration and a small molecular weight was added to carry out surface treatment, and the mixture was stirred at 350rpm for 60 minutes at room temperature to adsorb malonic acid on the particle surfaces, followed by washing and drying to prepare copper powder.

Comparative example 2

Commercial copper powder was obtained.

(Evaluation)

The BET specific surface area, the particle diameter, the carbon content, the oxygen content, the low-temperature sinterability, and the peak areas A1, A3, and A2 were confirmed by the measurement methods and the like described above for the copper powders of the above invention examples 1 to 5 and comparative examples 1 and 2. The results are shown in Table 1. For reference, a C1s spectrum obtained by XPS in invention example 5 is shown in fig. 1.

TABLE 1

As shown in Table 1, since the C/SSA of each of invention examples 1 to 5 was 0.07 or less and the peak area ratio (A2/A1) was 0.5 or more, it was found that the low-temperature sinterability was excellent from the result of the 5% shrinkage temperature obtained by TMA. Wherein the 5% shrinkage temperature obtained by TMA in invention examples 2 to 5 with a peak area ratio (A3/A1) of more than 0.3 is less than 280 ℃.

On the other hand, the C/SSA of comparative example 1 was greater than 0.07, and therefore the 5% shrinkage temperature obtained with TMA became high. The peak area ratio (A2/A1) of comparative example 2 was less than 0.5, and the 5% shrinkage temperature obtained with TMA was high.

Therefore, it can be said that the copper powders of invention examples 1 to 5 are excellent in low-temperature sinterability.

Claims

1. A copper powder, wherein,

The ratio C/SSA of the carbon content C to the BET specific surface area in m ²/g is 0.07 or less, the unit of the carbon content C is mass%,

In a C1s spectrum obtained by an X-ray photoelectron spectroscopy, a peak area ratio A2/A1 of an area A2 of a peak having a peak top in a range of 284eV to 289.2eV to an area A1 of a peak having a peak top in a range of 284eV to 284eV is 0.5 or more.

2. The copper powder of claim 1, wherein,

In a C1s spectrum obtained by an X-ray photoelectron spectroscopy, a peak area ratio A3/A1 of an area A3 of a peak having a peak top in a range of 284eV to an area A1 of a peak having a peak top in a range of 284eV to 284eV is 0.3 or more.

3. The copper powder according to claim 1 or 2, wherein,

The peak area ratio A2/A1 is 1.0 or less.

4. The copper powder according to claim 1 or 2, wherein,

The BET specific surface area of the copper powder was 0.5m ²/g～10.0m²/g.

5. The copper powder according to claim 1 or 2, wherein,

The average particle diameter calculated from the BET specific surface area is 0.05 μm to 2.00. Mu.m.

6. The copper powder according to claim 1 or 2, wherein,

The ratio O/SSA of the oxygen content O to the BET specific surface area is greater than 0.15, the oxygen content O is expressed in mass percent, and the BET specific surface area is expressed in m ²/g.