JPH01119602A - Production of silver-coated copper powder - Google Patents

Abstract

PURPOSE:To produce silver-coated copper powder having an excellent electrical conductivity, oxidation resistance and moisture resistance by dispersing the copper powder to a chelating agent soln., and adding a silver ion soln. thereto, then adding a reducing agent to the soln. to deposit silver films on the surface of the copper powder. CONSTITUTION:The copper powder is dispersed into the weakly acidic or neutral soln. of 1 or >=2 kinds of the chelating agents selected from ethylenediaminetetracetate, triethylenediamine and diethylenediaminepentaacetic acid. The amt. of the chelating agents to be used is 1-50wt.% of the weight of the copper powder in this case. The silver ion soln. consisting of a silver nitrate soln. is added to this liquid dispersion to accelerate reduction reaction; further, the reducing agent consisting of polyvalent carboxylic acids is added thereto at 0.1-10wt.% of the weight of the copper powder to cause the perfect reduction deposition, by which the silver films of 0.01-80wt.% of the weight of the copper powder are formed on the copper surfaces. The silver-coated copper powder utilizable for conductive fillers for a cold during conductive paste etc. is thereby obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silver-coated copper powder, and more specifically, to a method for producing silver-coated copper powder, and more specifically, it relates to a method for producing silver-coated copper powder, and more specifically, it can be used as a conductive filler for a low-temperature curing conductive paste. This invention relates to a method for producing silver-coated copper powder with excellent conductivity, oxidation resistance, and moisture resistance.

[Conventional technology]

Conventionally, there has been a conductive paste made by blending conductive metal powder, mainly silver powder, with an organic resin such as a phenolic resin. Since this paste can be fired at a low temperature of 300° C. or lower, it is used for through holes in printed wiring boards, wiring, and crossovers.

Conductive pastes using silver powder have excellent conductivity and oxidation resistance, but silver is expensive and difficult to obtain stably. On the other hand, when using copper powder, although copper is inexpensive and exhibits conductivity comparable to silver, it is easily oxidized and has problems with quality stability.

Copper powder coated with silver has been proposed as a conductive filler that compensates for the drawbacks of copper powder and has conductivity and oxidation resistance comparable to silver powder.

Generally, methods for producing this silver-coated copper powder include an electroless substitution plating method that utilizes a substitution reaction between copper and silver, and a reduction type electroless plating method that utilizes a silver mirror reaction of formalin. For example, a method in which metallic silver is precipitated by substitution on the surface of metallic copper powder using a silver complex salt solution of silver nitrate, ammonium carbonate, and disodium ethylenediaminetetraacetic acid (Japanese Patent Publication No. 57-197-1)
59283), a method of displacing and depositing metallic silver on the surface of metallic copper powder using silver nitrate, aqueous ammonia and a silver complex salt solution of sodium salt of ethylenediaminetetraacetic acid (Japanese Unexamined Patent Publication No. 61-3802), silver cyanide Methods such as using a bath have been proposed.

[Problem that the invention seeks to solve]

However, in the conventional method of displacing and depositing metallic silver on the surface of copper powder, even if the produced silver-coated copper powder has excellent initial conductivity, its properties deteriorate over time, and its moisture resistance is particularly poor. When using a silver cyanide bath, there is a high risk of using a powerful chemical, and when using formalin or the like for reduction and precipitation, both conductivity and moisture resistance are not good.

This invention was made based on the above-mentioned background, and its purpose is to provide excellent moisture resistance and oxidation resistance,
An object of the present invention is to provide a method for producing silver-coated copper powder that exhibits stable characteristics without being subject to changes over time and has good conductivity.

[Means for solving problems]

The above problems are solved by the method for producing silver-coated copper powder of the present invention.

That is, the method for producing silver-coated copper powder of the present invention involves dispersing copper powder in a chelating agent solution, adding a silver ion solution to this dispersion to promote a reduction reaction, and then adding a reducing agent to completely complete the process. This method is characterized by depositing a silver film on the surface of copper powder through reduction precipitation.

In a preferred embodiment of the invention, the amount of coated silver is 0.01 to 99% by weight, preferably 0.0% by weight of the copper powder.
1 to 80% by weight, more preferably 0.05 to 10% by weight
It can be done.

In a preferred embodiment of the present invention, the chelating agent used is one or more selected from ethylenediaminetetraacetate, triethylenediamine, and diethylenetriaminepentaacetic acid.

In a preferred embodiment of this invention, the amount of the chelating agent used is 0.1 to 80% by weight, preferably 1 to 80% by weight, based on the weight of the copper powder.
It can be 50% by weight, more preferably 2 to 25% by weight.

In preferred embodiments of this invention, the chelating agent solution can be weakly acidic or neutral.

This is because copper hydroxide is not formed in these pH ranges, and common chelating agents are difficult to form silver chelates.

In a preferred embodiment of the invention, the silver ion solution can be a silver nitrate solution, preferably an acidic silver nitrate solution.

In a preferred embodiment of this invention, the reducing agent used can be a polyhydric carboxylic acid, and the amount used is small, for example 0.01 to 20% by weight of the copper powder, preferably 0.01 to 20% by weight of the weight of the copper powder. It can be 1 to 10% by weight, more preferably 0.5 to 5% by weight.

This invention will be explained in more detail below.

Copper powder The copper powder that can be used in this invention is copper powder obtained by ordinary electrolytic method, reduction method, atomization method, mechanical pulverization method, etc., and its shape can be dendritic, acicular, spherical, or flaky. or granular, etc.

Furthermore, dendritic copper powder and granular or spherical copper powder can be mixed and used using a V-type mixer or the like.

Furthermore, before using copper powder in this invention, pre-treatments include sorting, cleaning with dilute sulfuric acid, degreasing with alkaline solution,
Although treatments such as de-scotting treatment can be performed, there is no need to perform these treatments in the present invention.

Chelating Agent Solution The chelating agent used in this invention forms a stable complex with copper ions and is preferably one that does not easily react with silver ions. As such, for example,
Ethylenediaminetetraacetate, triethylenediamine, diethylenetriaminepentaacetic acid, N, N, N', N'
-tetraethylethylenediamine, diethylenediamine, phenanthroline, ethylenedioxybis(ethylamine')-N,N,N',N'-tetraacetic acid, nitrilotriacetic acid, picolinic acid, and combinations thereof. Among these, a preferred chelating agent is ethylenediaminetetraacetate (hereinafter referred to as EDTA).
and triethylenediamine (hereinafter abbreviated as Trien), diethylenetriaminepentaacetic acid (hereinafter referred to as DTP),
(abbreviated as A), or a combination thereof. This is because the copper chelate complex is superior in terms of stability, reagent cost, workability, etc. Note that since EDTA is inexpensive, EDTA and Trien are used as representative examples of chelating agents in the Examples described below.

The chelating agent is used in the method of this invention after being dissolved in a suitable solvent. Examples of the solvent include water. Water of various levels can be used depending on the desired performance of the copper powder. For example, industrial water can be used, but ion exchange water or pure water is preferable.

The preferred amount of the chelating agent used is 0.1 to 0.1 to the weight of the copper powder.
80% by weight, 26% by weight, preferably 1-50% by weight, more preferably 2-25% by weight. Depending on the amount used, the copper hydroxide or oxide on the surface of the copper powder can be converted into a copper chelate complex, and the surface of the copper powder can be quickly and completely coated with silver.

Various additives can be added to the chelating agent solution as necessary. These include brighteners, lead chloride to improve ductility, minimal amounts of potassium ferrocyanide, and dispersants such as sodium laurate.

The liquid nature of the chelating agent solution is preferably acidic, particularly weakly acidic or neutral. This is because such liquid properties can prevent the formation of hydroxides on the surface of the copper powder, and the pH range is such that silver ions are difficult to form complexes.

Silver Ion Solution The silver ion solution used in the method of this invention is arbitrary as long as it does not contradict the purpose of this invention. A typical silver ion solution includes a silver nitrate aqueous solution.

The silver ion solution used in this invention is preferably neutral or weakly acidic. In the ammoniacal silver nitrate solution used in electroless plating, silver ions are made into a stable ammonia complex, but its alkalinity may cause the formation of copper hydroxide on the surface of the copper powder. be.

The concentration of the silver nitrate solution is not particularly limited in the present invention, but is adjusted to, for example, about 10 to 200 g/II). Water of various levels can be used depending on the desired performance of the copper powder, for example, industrial water can be used, but preferably ion exchange water or pure water. Various reducing agents can be used as the reducing agent capable of. Preferred reducing agents are weak reducing agents. A silver coating is formed by displacement precipitation due to the addition of silver ions, but oxides (Cub, CuO, Ago, Ag
This is because 20) is generated and it is necessary to reduce it, but also to prevent copper complex ions from being reduced.

Weak reducing agents that can be used in this invention include reducing organic compounds, such as carbohydrates such as glucose, malonic acid, succinic acid, glycolic acid, lactic acid, malic acid, tartaric acid, oxalic acid. These include polyhydric carboxylic acids and their salts, and aldehydes such as formalin.

The amount of reducing agent used is sufficient for reduction, and can be appropriately selected depending on the copper powder, chelating agent, silver ion solution, reaction conditions, etc. used. For example, the amount of the reducing agent used is 0.01 to 20% by weight, preferably 0.1 to 10% by weight, and more preferably 0.5 to 5% by weight based on the weight of the copper powder.

Manufacturing method The method for manufacturing silver-coated copper powder of the present invention involves dispersing copper powder in a chelating agent solution, adding a silver ion solution to this dispersion (slurry) to promote a reduction reaction, and then adding a reducing agent. The copper powder is completely reduced and precipitated to deposit a silver film on the surface of the copper powder.

FIG. 1 shows a flow diagram of a manufacturing example according to the present invention.

The reaction conditions (reaction time, reaction temperature, atmosphere, etc.) of this displacement precipitation reaction and reduction precipitation reaction are determined based on the desired characteristics of the copper powder,
The selection can be changed as appropriate depending on the type of reagent.

For example, it is desirable to add a silver ion solution to a copper powder dispersion while stirring to promote the reaction.

After the silver ions are precipitated by substitution and precipitated by reduction, the silver-coated copper powder can be washed with purified water or the like, filtered, and further dried, if necessary. Cleaning can usually be carried out by pouring purified water onto the copper powder or stirring it in purified water, and drying can be carried out by heating it in a drying oven in an inert atmosphere or using a volatile water-soluble solution such as methanol. This can be done by washing with a liquid and then evaporating the liquid.

The silver-coated copper powder obtained by this invention can be used for various purposes, and can be used as a conductive filler for conductive paints, conductive pastes, conductive resins, and the like.

[For production]

Silver-coated copper powder (')' of this invention configured as above
A is manufactured using the following mechanism.

When copper powder is applied to a chelating agent solution, the chelating agent forms a very stable complex with copper ions, and forms compounds such as copper oxides and copper compounds with organic substances (suma-soto). also breaks this bond to form a complex. Therefore, it is possible to remove trace amounts of copper ions in the solution (without leaving traces) and to remove contamination (oxide film, etc.) on the surface of the copper powder.In this way, the surface of the copper powder to be coated with silver can be well cleaned. ,
The most reactive active sites can be exposed to the surface.

When a silver ion solution is added to a slurry of activated copper powder, a substitution reaction occurs instantly and silver is deposited on the copper surface. This is because, in addition to the fact that the copper powder is activated, the silver ions used in this invention are in an uncomplexed and unstable state.

As mentioned above, a silver coating is formed by displacement precipitation due to the addition of silver ions, but oxides (CuO-Cu20, Ago.

A g 20 ) is generated, and this by-product may impair the oxidation resistance of the copper powder. In this invention, a reducing agent is then added to reduce and remove this by-product.

The weak reducing agent used in the preferred embodiment of this invention includes:
Although the remaining silver ions are reduced, even the copper complex ions are not reduced.

As described above, in this invention, silver precipitation occurs through a substitution reaction and a reduction reaction, and this combination provides excellent properties to the silver-coated copper powder.

〔Effect of the invention〕

The following effects can be obtained by this invention.

(a) It is possible to produce silver-coated copper powder that has excellent moisture resistance and oxidation resistance, exhibits stable characteristics without being subject to changes over time, and has good electrical conductivity.

(b) Conventionally, cleaning and degreasing are performed as pre-treatments for copper powder, but during these pre-treatment cleaning and filtration steps, hydroxides and oxides may be formed on the surface of the copper powder, causing The effect of processing is halved. but.

In this invention, active copper powder can be prepared for treatment with a chelating agent solution without requiring any particular pretreatment such as washing. Therefore, workability is good and process costs can be reduced.

(c) In the silver-coated copper powder of the present invention, there is no limit to the amount of silver coating; for example, even if it is only 1%, the properties are not affected.

This is because the surface of the copper powder is washed with the chelating agent, and silver is reliably deposited and coated on the active surface. Therefore, the amount of silver used can be reduced.

(d) Conventional copper powder requires storage under an inert atmosphere such as a nitrogen atmosphere, but in the present invention, it can be stored without change even in adverse environments of high temperature and high humidity.

(e) All the reagents used are inexpensive and in small amounts, and the method of the present invention has high industrial value.

〔Example〕

This invention will be specifically explained by examples.

Example 1 Copper powder (manufactured by Mitsui Mining & Co., Ltd., MFP-1110) 493.3
gr was dispersed in a 4.8 g bath containing 5 g of EDTA and stirred at 20 rpm for about 5 minutes.

A silver nitrate solution prepared by dissolving 15.7 g of silver nitrate in 200 mg of pure water was added to this dispersion in a short period of time while stirring. The liquid temperature is 25 to 50°C, and is not particularly limited.

Stirring was continued for approximately 30 minutes.

Then, 10 g of tartaric acid as a reducing agent was added.

Furthermore, stirring was continued for about 30 minutes.

Next, filter and wash with pure water until the filtrate becomes clear.
It was evacuated with a vacuum pump for 1 hour and placed in a dryer at 70°C.

Note that drying in the air is sufficient.

The yield of silver-coated copper powder was 492.5 g, and the yield was 98
．． 5%, and the silver content was 2.0%.

A paste was prepared by kneading 50 g of the obtained copper powder and 11.26 g of a phenolic resin solution having the composition shown below in a three-roll mill 30 times. The resulting paste was applied onto a paper phenol substrate by screen printing. This paste was dried in air at 160° C. for 30 minutes to form a circuit board.

Phenol resin solution composition (wt%) Phenol resin 49.4 Methylcarpitol 37.3 Toluene
The specific resistance value of the 4.5 acetone 8°8 coating film was 1.94×10″Ωam, indicating extremely good electrical conductivity. The 90° pull strength measured by soldering to this coating was 1.29 kg/m.
It was.

In addition, in order to examine the moisture resistance and oxidation resistance of copper powder, 100 g of the obtained powder was stored in a constant temperature and humidity chamber at 40°C and 95% relative humidity for 24 hours, taken out, and made into a paste using the above method. The specific resistance value was set at 1111 J and its rate of change was determined. The specific resistance value is 1. 93X10-4Ω (1,
It was observed that there was no change at all. Furthermore, it was observed that the oxygen attack rate of the powder did not change at all before and after the moisture resistance test.

Similarly, changes in resistance, heat resistance, and high temperature and humidity resistance of the coating film were investigated. As a result, there were no problems with heat resistance. 85℃
, only slight deterioration was observed in the aging characteristics at a relative humidity of 95%.

The specific resistance value when left for 100 hours at 85° C. and 95% relative humidity was 2.86×10′Ωcm, indicating extremely good conductivity.

Table 1 summarizes the measurement results.

Example 2 Silver-coated copper powder of silver-coated mounting piece 196 was produced by the same operation as in Example 1.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

The results show that all properties are particularly excellent, and even with a silver coating of only 1%, the properties are satisfactory.

Example 3 A silver-coated copper powder having a silver coverage of 2% was produced in the same manner as in Example 1 except that 45 g of Trien was used as a chelating agent and 2 g of tartaric acid was used as a reducing agent.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

From this result, it can be seen that although the initial characteristics are somewhat inferior, the results are excellent in all characteristics.

Comparative Example 1 A silver-coated copper powder having a silver coating of 2% was produced by the same operation as in Example 1 except that no reducing agent was used.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

From this result, it was found that the aging resistance of the copper powder and the coating film was somewhat inferior. This may have an adverse effect on quality stability.

Comparative Example 2 Silver-coated copper powder having a silver wave 5f amount of about 2% was produced by the same operation as in Example 1 except that an ammoniacal silver nitrate solution in which silver ions were complexed was used.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

From this result, it was found that the initial characteristics of the copper powder and coating film, solder adhesion, moisture resistance, and oxidation resistance of the copper powder and coating film were inferior.

Comparative Example 3 By the same operation as Comparative Example 2, silver wave ff1ffi was approximately 1%.
silver-coated copper powder was produced.

The properties of the obtained copper powder were determined in the same manner as in Example 1.
The results are shown in Table 1.

The results of the moisture resistance test showed that although the initial properties were good, the changes over time were large and the moisture resistance was poor. Therefore, it was found that silver-coated copper powder is particularly excellent in the use of acidic silver nitrate, which is a preferred embodiment of the present invention.

Comparative Example 4 Silver-coated copper powder was produced according to a conventional production method (Japanese Patent Publication No. 57-59283).

That is, 500 g of copper powder from which the oxide film was removed with dilute sulfuric acid as a pretreatment was mixed with 1 ml of silver nitrate at room temperature while stirring at 20 rpm.
A silver ion solution prepared by mixing 32 cc of an aqueous solution of 6.24 g (liquid A) and liquid B in which 81.2 g of ammonium carbonate and 65 g of EDTA-3Na salt were dissolved in 350 cc of pure water was mixed with 5 ml of silver ion solution.
The mixture was added for 60 minutes and reacted for 60 minutes.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

The test results showed that although the initial properties were good, the changes over time were large and the oxidation resistance and moisture resistance were poor.

Comparative Example 5 Silver-coated copper powder was produced according to a conventional production method (Japanese Unexamined Patent Publication No. 61'-3802).

That is, 500 g of copper powder, which had been degreased with alkali as a pretreatment and whose oxide film was removed with dilute sulfuric acid, was added to pure water 11).
The mixture was dispersed under stirring at 00 rpm. 15.19 g of silver nitrate and 101.2 g of EDTA.2Na salt were dissolved in 2 liters of pure water, and 147 ml of ammonia (25 wt%) was added to adjust the total amount to 2.5 liters. This silver ion solution was added to the copper powder dispersion while stirring at 400 rpm.
The mixture was added over a period of 1 minute and reacted for 1 hour. Next, it was filtered, and the filtrate was washed with pure water until the pH became 7, and after suction for 1 hour, it was dried for 1 hour in a vacuum dryer at 50° C. to obtain silver-coated copper powder.

The properties of the obtained copper powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

The test results show that the initial properties are good, but the aging is significant (oxidation resistance and moisture resistance are poor).

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of the manufacturing method according to the present invention. Applicant's agent: Mr. Sato ``Hikidu'' Figure 1

Claims (1)

[Claims] 1. Copper powder is dispersed in a chelating agent solution, a silver ion solution is added to the dispersion, and a reducing agent is then added to deposit a silver film on the surface of the copper powder. Method for producing silver-coated copper powder. 2. The method for producing silver-coated copper powder according to claim 1, wherein the amount of coated silver is 0.01 to 80% by weight of the weight of the copper powder. 3. Production of silver-coated copper powder according to claim 1 or 2, in which the chelating agent is one or more selected from ethylenediaminetetraacetate, triethylenediamine, and diethylenetriaminepentaacetic acid. Law. 4. The amount of chelating agent used is 1 to 50% by weight of the copper powder.
A method for producing silver-coated copper powder according to claim 3. 5. The method for producing silver-coated copper powder according to claim 4, wherein the chelating agent solution is weakly acidic or neutral. 6. The method for producing silver-coated copper powder according to any one of claims 1 to 5, wherein the silver ion solution is a silver nitrate solution. 7. The method for producing silver-coated copper powder according to claim 6, wherein the silver nitrate solution is acidic. 8. The method for producing silver-coated copper powder according to any one of claims 1 to 7, wherein the reducing agent is a polyhydric carboxylic acid. 9. The method for producing silver-coated copper powder according to item 8, wherein the amount of the reducing agent used is 0.1 to 10% by weight based on the weight of the copper powder.