WO2023058798A1 - Multilayer copper particles having excellent corrosion resistance - Google Patents

Abstract

The purpose of the present invention is to provide copper particles having formed on the surface thereof a nickel metal layer having excellent electrical conductivity as well as excellent corrosion resistance and adhesiveness to the copper particles. In order to achieve said purpose, the present invention may provide multilayer copper particles comprising a second layer which is formed on a first layer and comprises nickel.

Description

Multi-layered copper particles with excellent corrosion resistance

The present invention relates to a copper particle having a multi-layered structure having a nickel coating layer on the surface. In particular, a bonding layer containing silver oxide is first formed on the surface of the copper particle, and then a nickel metal layer with improved compactness and bonding property is formed on the surface, thereby improving electrical conductivity and It relates to copper particles having a multilayer structure with improved oxidation resistance and a method for producing the same.

Conductive particles are widely used in electronic materials. Among them, copper particles have high conductivity and are highly competitive in price, so they are widely used in films, adhesives, and coating slurries that require electrical conductivity in many electronic parts.

However, these copper particles have high electrical conductivity close to that of silver, and are very low in price compared to silver, but have poor oxidation resistance. Due to the problem of low reliability due to such low oxidation resistance, the field to which copper particles can be applied is very limited.

Therefore, if a protective coating layer having high oxidation resistance and electrical conductivity can be formed on the surface, this low reliability problem can be solved. As such a protective coating layer, a coating layer made of nickel or silver is applied.

The key to such a coating layer is that pinholes or low-density protective coatings should not be formed. This is because if there are pinholes or low density in the protective coating layer, rapid oxidation of copper particles, which are cores, may occur.

Therefore, the important point for copper particles with a protective coating layer is the formation of a defect-free protective coating layer with a tight density.

An object of the present invention is to provide a copper particle having a nickel metal layer having excellent electrical conductivity and excellent corrosion resistance and bonding strength with the copper particle at the same time.

Another object of the present invention is to provide a method for manufacturing composite copper particles capable of forming a nickel metal layer having excellent electrical conductivity and excellent corrosion resistance and bonding strength with copper particles on the surface of copper particles at low cost.

In order to achieve the above object, the present invention provides a copper particle having a multi-layer structure including a first layer containing silver oxide formed on the surface of the copper particle and a second layer containing nickel while being formed on the first layer. can do.

In one embodiment of the present invention, the shape of the copper particles is any one selected from the group consisting of a spherical shape, a plate shape, a dendrite shape, or a combination thereof, and the particle size of the copper particles is analyzed by a laser scattering type particle size analyzer When D ₅₀ may be in the range of 0.1 ~ 100㎛.

In one embodiment of the present invention, the first layer further includes metallic silver, and the molar ratio of the silver element in the silver oxide to the silver element in the metallic silver (Ag ^{x +} /Ag ⁰ ( 0 < x ≤ 3 )) It may range from 10 to 100.

In one embodiment of the present invention, the first layer may further include tin.

In one embodiment of the present invention, the first layer may include a tin layer formed on the surface of the copper particle and a silver oxide layer formed on the tin layer.

In one embodiment of the present invention, the content of silver included in the first layer may be 10 to 1,000 ppm based on the total weight of the oxide-resistant copper particles.

In one embodiment of the present invention, the first layer may have a discontinuous island shape on the surface of the copper particle.

In one embodiment of the present invention, the second layer may further include phosphorus together with the nickel, and the amount of phosphorus in the second layer may be 0.1 to 13% by weight.

A method for manufacturing a multi-layered copper particle according to the present invention includes (a) forming a first layer of coating silver oxide on the surface of the copper particle, and (b) electrolessly plating nickel on the first layer to form a second layer containing nickel. It may include forming a layer.

In addition, in step (a), tin may be coated with silver oxide at all times.

In addition, before step (a), a step of forming a tin layer may be further included.

The multi-layered copper particles according to the present invention are inexpensive and have excellent electrical conductivity and corrosion resistance, so that they can be applied to various electronic parts that require electrical conductivity, and the bonding strength of the surface metal layer is excellent, thereby reducing the weight of the applied parts and improving conductivity and reliability. be able to achieve

In addition, the method for manufacturing multilayered copper particles provided by the present invention enables mass production of multilayered copper particles having excellent conductivity and reliability through a low-cost process.

1 is a scanning electron microscope image of multi-layered copper particles according to Examples and Comparative Examples according to the present invention.

Figure 2 shows the analysis results according to the X-ray photoelectron spectroscopy (XPS) for the multi-layered copper particles in one embodiment according to the present invention.

Hereinafter, the configuration and operation of embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, when a certain part 'includes' a certain component, this means that it may further include other components without excluding other components unless otherwise stated.

Copper particles can be made into particles of various shapes and sizes. However, since oxidation resistance, corrosion resistance, chemical resistance, etc. are very low due to the nature of the material, it cannot be prevented from rapidly deteriorating electrical conductivity over time and the use environment. To overcome this, if a conductive metal layer is formed on the surface as a protective layer, it is possible to impart a high level of oxidation resistance to copper particles of various shapes and sizes. Nickel or silver is often used as such a protective layer. Since silver is a precious metal and has a high price problem, many attempts have been made to form nickel as a protective layer.

On the other hand, when nickel is applied as the protective layer, it is important that the nickel protective layer is densely formed without defects such as pinholes, since corrosion proceeds rapidly around these defects.

To this end, the present invention may provide a copper particle having a multilayer structure including a first layer containing silver oxide formed on the surface of the copper particle and a second layer containing nickel formed on the first layer.

The inventors of the present invention found that when a bonding layer containing silver oxide is formed before the formation of the nickel protective layer, the density of the final nickel protective layer is improved and the bonding force with copper particles is also increased. By forming a bonding layer containing silver oxide in the middle rather than forming a protective layer containing silver oxide, it is possible to develop copper particles having a multilayer structure in which a nickel protective layer is densely formed without pinholes.

Copper particles serving as cores in the present invention may be particles of various shapes, and may be any one selected from the group consisting of spherical, plate-shaped, dendrite-shaped, or combinations thereof. Copper particles used in various industrial fields may be spherical, plate, dendrite, etc. depending on the field to which they are applied, and they may be mixed and used. On the other hand, when the size of these particles is analyzed with a laser scattering type particle size analyzer, D ₅₀ may be in the range of 0.1 to 100 μm, where D ₅₀ refers to the particle size when the cumulative percentage of the particles reaches 50%. . When the particle size of the copper particles is less than 0.1 μm based on D ₅₀ , the aggregation between the particles is severe, making it difficult to handle and difficult to form a surface nickel layer due to the increased specific surface area. On the other hand, if the particle size exceeds 100 μm, the weight of the particles increases, making it difficult to smoothly apply them to electronic parts.

In the present invention, the first layer containing silver oxide may further include tin. Tin is an element used to induce silver oxide to be smoothly attached to the surface of copper particles, and when the coating operation is performed in an aqueous solution, copper of silver element It aids adhesion to the particle surface. Such tin may form a first layer together with silver oxide, or may be formed between the first layer containing silver oxide and the surface of the copper particle.

In the present invention, the first layer including silver oxide may further include metal silver together with the silver oxide, and when metal silver is further included, bonding with nickel, which is a metal included in the second layer, may be stronger. Silver oxide strengthens the bond with copper, and metal silver strongly bonds with the silver oxide and at the same time provides a strong bond with nickel, which is the same metal. As a result, the bonding force between the second layer containing nickel and the copper particles is further strengthened. do.

At this time, it is preferable that the molar ratio (Ag ^x+ /Ag ⁰ ( 0 < x ≤ 3 )) of the silver element in the silver oxide to the silver element of the metal silver in the first layer is in the range of 10 to 100.

As described above, although the inclusion of metallic silver strengthens the bond between the first layer containing silver oxide and the second layer containing nickel, if the ratio of the silver element in the metallic silver compared to the silver element in the silver oxide is too high, This is not preferable because the bonding force of the first layer with the surface of the copper particles through the silver oxide is lowered. Therefore, the molar ratio of the silver element in the metallic silver to the silver element in the silver oxide is preferably 10 to 100 so that the ratio of the silver element in the silver oxide is higher. Measurement of this molar ratio can be measured by X-ray Photoelectron Spectroscopy (XPS).

Here, the oxidation number of silver in silver oxide can be from +1 to +3, and since the oxidation number of silver in the amorphous phase may not be an integer, the oxidation number of silver in silver oxide can exceed 0 and be 3 or less.

In addition, the amount of silver included in the first layer may be 10 to 1,000 ppm of the total weight of the multi-layered copper particles.

This is because the amount of metallic silver or silver oxide formed in the first layer must be greater than a certain amount to provide a satisfactory binding force to the second layer, and an excessively large amount is undesirable because process costs increase. More preferably, it may be 10 to 500 ppm.

Also, in the present invention, the first layer may have an island shape discontinuously formed on the surface of the copper particle. The first layer is a layer that reinforces the bonding strength of the second layer that imparts oxidation resistance to copper particles, which are cores, and can sufficiently provide bonding strength to the second layer even if it is in the form of a discontinuous island.

Meanwhile, the first layer may be in the form of a continuous film, in which case the first layer occupies at least 50% of the surface area of the copper particles. This is because, even in the case of a continuous film form, sufficient binding force can be provided to the second layer only when it is at least 50% or more of the particle surface area.

A second layer containing nickel, a metal having excellent oxidation resistance, is formed on the first layer containing silver oxide. Since nickel has excellent oxidation resistance and chemical resistance and at the same time relatively high electrical conductivity, the multi-layered copper particles have excellent electrical conductivity and reliability at the same time.

The second layer containing nickel may further include phosphorus as well as nickel. Inclusion of phosphorus lowers electrical conductivity somewhat, but improves chemical resistance and oxidation resistance, so when used in parts where reliability is important, It is preferable to include phosphorus together with nickel in the second layer. In the case of containing phosphorus, the content of phosphorus in the second layer is preferably 0.1 to 13.0% by weight. If it is too low, the desired improvement in chemical resistance and oxidation resistance is not achieved, and if it contains more than 13% by weight of phosphorus, sufficient electricity This is because conductivity cannot be obtained.

On the other hand, since a low phosphorus content is advantageous in terms of electrical conductivity, the phosphorus content in the nickel layer is preferably 0.1 to 6% by weight in areas where electrical conductivity is important.

In addition, in the present invention, a copper particle having a multi-layer structure including (a) forming a first layer of coating silver oxide on the surface of the copper particle, and (b) forming a second layer of electroless plating nickel on the first layer. A manufacturing method can be provided.

A first layer containing silver oxide is formed on the surface of the copper particle, and tin may be coated together with the silver oxide. Tin can increase the binding force of silver oxide on the surface of copper particles.

In addition, for more precise control, a tin layer may be first formed on the surface of the copper particle, and then a first layer containing silver oxide may be formed.

Formation of the first layer containing silver oxide may be performed in an alkaline aqueous solution having a pH of 8 or higher. This is because silver oxide is well formed in an alkaline atmosphere of pH 8 or higher. More preferably, it may be made in an aqueous solution in the pH range of 8 to 10.

In addition, in the method for manufacturing copper particles having a multilayer structure, after step (a) and before step (b), the copper particles having the first layer containing the silver oxide are stirred in an aqueous solution having a pH of 8 to 11 and a temperature of 20 to 80 ° C. A post-treatment step of adjusting the amount of silver oxide may be further included.

When the first layer is formed in an aqueous solution, silver ions in the aqueous solution are reduced and may be attached to the surface of the copper particles as metallic silver rather than silver oxide. If the ratio of the metal silver is too high, it is undesirable because the bonding force between the copper particles and the second layer may be lowered. Therefore, the amount of silver oxide can be controlled by treating the silver oxide in an alkali aqueous solution at an appropriate temperature to increase the silver oxide content to a desired level.

In this way, by adjusting the amount of silver oxide and forming a second layer containing nickel having excellent oxidation resistance, it is possible to provide conductive and highly reliable multi-layered copper particles.

Hereinafter, preferred embodiments of the present invention are attached in order to fully understand the present invention.

It demonstrates with reference to drawings.

The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the following examples may be modified in many different forms, and the scope of the present invention It is not limited to the examples below. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the spirit of the invention to those skilled in the art.

[Example 1]

20 g of a degreasing agent (product name: A-Screen, Okuno Chemical Co., Japan) was added to 100 g of deionized water, and the temperature was raised to 60°C. 20 g of spherical copper particles having a D of ₅₀ of 20 μm were added thereto, and a pretreatment was performed for 30 minutes while stirring to remove organic matter and impurities attached to the surface of the copper particles. Thereafter, the copper particles were recovered, washed three times by stirring in 100 g of deionized water, and recovered.

The recovered copper particles were added to a silver nitrate solution in which 0.15 g of silver nitrate (AgNO ₃ ) was dissolved in 100 g of deionized water and stirred. At this time, 28% concentration of ammonia water was added dropwise to adjust the pH to 9.1.

The temperature was maintained at 40°C and stirred for 1 hour to form a silver oxide layer. After 1 hour, it was collected by filtration, and then washed three times by stirring in 200 g of deionized water, and then recovered. A portion of the powder having the silver oxide layer was collected and surface analysis was performed through X-ray Photoelectron Spectroscopy (XPS).

The powder formed up to the silver oxide layer was recovered, and a nickel coating layer was formed using an electroless plating method. In 300 g of deionized water solution, 20 g of nickel chloride (NiCl ₂ 6H ₂ O), 10 g of sodium acetate, 5 g of maleic acid, 30 g of sodium hypophosphate as a reducing agent, and 3 lead acetate The powder formed up to the silver oxide layer was added to the nickel plating solution composed of ㎖, stirred, and electroless plating was performed at 70 to 90 ° C. for 2 hours.

[Example 2]

A pretreatment for removing organic matter or impurities attached to the surface of the copper particles was performed in the same manner as in Example 1, and then a tin layer was formed. The tin layer was formed by adding copper particles to an aqueous solution in which 1.5 g of stannous chloride (SnCl ₂ 2H ₂ O) and 1 ml of hydrochloric acid (HCl 35% solution) were dissolved in 100 g of deionized water and stirred for 30 minutes. The temperature of the aqueous solution was maintained at 35°C. Thereafter, the first layer containing silver oxide and the second layer containing nickel were formed in the same manner as in Example 1.

[Example 3]

Pretreatment and formation of the first layer were performed in the same manner as in Example 1. After that, the formation of the nickel layer was performed using 300 g of deionized water solution, 20 g of nickel chloride (NiCl ₂ 6H ₂ O), 10 g of sodium acetate, 3 g of ammonia water, 10 g of sodium hypophosphate and 10 g of hydrazine as a reducing agent. , The powder formed up to the silver oxide layer was added to the nickel plating solution composed of 1 ml of lead acetate, stirred, and electroless plating was performed at 40 to 60 ° C. for 1 hour.

[Comparative Example 1]

Copper particles were pretreated in the same manner as in Example 1. Thereafter, electroless plating was directly performed without forming a silver oxide layer to form a second layer containing nickel. Electroless plating of nickel was performed in the same manner as in Example 1.

[Comparative Example 2]

In the same manner as in Example 1, a first layer containing silver oxide was formed on the surface of the copper particle. Thereafter, ascorbic acid was added to the aqueous solution to convert silver oxide on the surface into a metallic silver state, and then electroless plating was performed to form a second layer containing nickel. Electroless plating of nickel was performed in the same manner as in Example 1.

After the first layer was formed on the multi-layered copper particles thus formed, the silver element ratio analysis of silver oxide and metallic silver, analysis of nickel content and phosphorus content, and observation of the coating state through a scanning electron microscope (SEM) were performed. The silver element ratio was analyzed by taking a sample after forming the first layer and using XPS. Nickel content and phosphorus content were analyzed through an inductively coupled plasma mass spectrometer (ICP).

Reliability is measured through a reflow test in which copper particles made in Examples and Comparative Examples are mixed with an acrylic binder in a certain amount, applied on a polyimide film, dried, held on molten lead for 30 seconds, and then conductivity is measured. evaluated.

The results are shown in Table 1 below. Here, the nickel content represents the weight percent occupied by the nickel element based on the copper particles of the entire multilayer structure, and the phosphorus content represents the content in the second layer containing nickel as a weight percent.

	Ag x + /Ag 0	Ni content (wt%)	P content (wt%)	coating condition	Corrosion resistance (mΩ)
Example 1	40.5	19.5	9.5	Good	60
Example 2	92.4	20.1	10.5	Good	45
Example 3	33.6	19.8	3.1	Good	33
Comparative Example 1	-	-		error	265
Comparative Example 2	0.10	19.1	9.7	error	89
copper particles	-	-		-	not measured

1 shows a scanning electron micrograph of multi-layered copper particles according to an embodiment. 1 (a) and (b) are scanning electron microscope images of samples according to Examples 1 and 2, respectively, and FIG. 1 (c) and (d) are scanning electron microscope images of samples according to Comparative Examples 1 and 2. This is an electron microscope image.

Samples according to Examples 1 and 2 both show that a dense coating layer was formed, but in the case of Comparative Example 1 without an intermediate silver oxide layer, it could be seen that a non-dense nickel layer was formed. In addition, when the first layer containing most of the metal silver was formed, the nickel layer was stably formed, but it could be seen that there was a pinhole in the middle.

FIG. 2 is a result of measuring a ratio of silver elements of silver oxide and metallic silver in a first layer in a sample according to Example 21. FIG. As a result of the XPS, it is possible to measure the silver ratio in the reduced state and the silver ratio in the oxidized state through the peak ratio. Their molar ratio (Ag ^x+ /Ag ⁰ ) in Example 1 was 92.4.

On the other hand, as shown in Table 1, corrosion resistance was evaluated through a reflow test. In Examples 1 to 3, the resistance of the film using the multi-layered copper particles was good even after the reflow test, but Comparative Examples 1 and 2 with unstable coating layer formation In , the resistance increased significantly, and in the film using general copper particles without a protective layer, the resistance was too high to be measured.

Claims (9)

1. A first layer containing silver oxide formed on the surface of the copper particle;

   A copper particle having a multilayer structure, comprising a second layer formed on the first layer and containing nickel.
2. According to claim 1,

   The shape of the copper particles is any one selected from the group consisting of a spherical shape, a plate shape, a dendrite shape, or a combination thereof, and when the particle size of the copper particles is analyzed with a laser scattering type particle size analyzer, D ₅₀ is 0.1 to 100. Multi-layered copper particles, in the micrometer range.
3. According to claim 1,

   The first layer further comprises metallic silver, and the molar ratio of silver element in the silver oxide to silver element in the metallic silver (Ag ^{x +} /Ag ⁰ ( 0 < x ≤ 3 )) is in the range of 10 to 100. copper particles in the structure.
4. According to claim 1,

   The multilayer structure of the copper particles, wherein the first layer further includes tin.
5. According to claim 1,

   The content of silver included in the first layer is 10 to 1,000 ppm of the total weight of the oxidation-resistant copper particles.
6. According to claim 1,

   The second layer further comprises phosphorus together with the nickel, the multi-layered copper particles.
7. According to claim 6,

   In the second layer, the phosphorus is 0.1 to 13% by weight, copper particles having a multilayer structure.
8. (a) forming a first layer of coating silver oxide on surfaces of copper particles; and

   (b) electroless plating nickel on the first layer to form a second layer containing nickel.
9. According to claim 8,

   A method of manufacturing copper particles having a multilayer structure, further comprising forming a tin layer before the step (a).

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