KR20240050418A - Multi-layered copper particles with excellent corrosion resistance - Google Patents

Abstract

The purpose of the present invention is to provide copper particles having a nickel metal layer formed on the surface, which has excellent electrical conductivity and at the same time excellent corrosion resistance and bonding power with copper particles. In order to achieve the above object, the present invention can provide copper particles with a multilayer structure including a second layer containing nickel and formed on the first layer.

Description

Multi-layered copper particles with excellent corrosion resistance

The present invention relates to a multi-layered copper particle 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 density and bonding properties is formed on the surface to improve electrical conductivity and It relates to copper particles with a multilayer structure with improved oxidation resistance and a method of manufacturing the same.

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

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

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

The key to this coating layer is that no pinholes or a low-density protective coating layer are formed. This is because pinholes or a low-density protective coating layer can cause rapid oxidation of the core copper particles.

Therefore, the important point in copper particles with a protective coating layer is the formation of a dense, defect-free protective coating layer.

The purpose of the present invention is to provide copper particles having a nickel metal layer formed on the surface, which has excellent electrical conductivity and at the same time excellent corrosion resistance and bonding power with copper particles.

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

In order to achieve the above object, the present invention provides a copper particle with a multilayer structure comprising 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. can do.

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

In one embodiment of the invention, the first layer further comprises metallic silver, and the molar ratio of elemental silver in the silver oxide to elemental silver in the metallic silver (Ag ^x+ /Ag ⁰ (0<x ≤3)) This can be in the range of 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 oxidation-resistant copper particles.

In one embodiment of the present invention, the first layer may be in the form of discontinuous islands on the surface of the copper particle.

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

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

Additionally, tin can always be coated with silver oxide in step (a).

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 they can be applied to various electronic components that require electrical conductivity, and the bonding power of the surface metal layer is excellent, making the applied components lighter and improving conductivity and reliability. It can be achieved.

In addition, the method for manufacturing copper particles with a multi-layer structure provided by the present invention makes it possible to mass-produce copper particles with a multi-layer structure with excellent conductivity and reliability through a low-cost process.

1 is a scanning electron microscope image of multilayer-structured copper particles according to Examples and Comparative Examples according to the present invention.
Figure 2 shows analysis results using X-ray Photoelectron Spectroscopy (XPS) on multilayered copper particles in an embodiment according to the present invention.

Best mode for carrying out the invention

Hereinafter, the configuration and operation of an embodiment of the present invention will be described with reference to the attached drawings. In describing the present invention below, if a detailed description of a related known function or configuration is judged to unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, when a part is said to 'include' a certain component, this does not mean excluding other components, but may include other components, unless specifically stated to the contrary.

Copper particles can be made into particles of various shapes and sizes. However, due to the nature of the material, oxidation resistance, corrosion resistance, and chemical resistance are very low, so it is impossible to prevent electrical conductivity from rapidly decreasing depending on the usage environment and the passage of time. To overcome this, forming a conductive metal layer as a protective layer on the surface can provide a high level of oxidation resistance to copper particles of various shapes and sizes. Nickel or silver is often used as this protective layer, but silver is a precious metal and has a high price, so there are many attempts to form nickel as a protective layer.

Meanwhile, when nickel is applied as a protective layer, it is important that the nickel protective layer is formed densely without defects such as pinholes, because if there is a defect such as a pinhole, corrosion progresses rapidly around it.

To this end, the present invention can provide copper particles with 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 forming the nickel protective layer, the density of the final nickel protective layer is improved and the bonding strength with the copper particles is also increased. From this, nickel is directly deposited on the surface of the copper particles. By forming a bonding layer containing silver oxide in the middle rather than forming a protective layer containing silver oxide, it was possible to develop copper particles with a multi-layer structure in which the nickel protective layer is densely formed without pinholes.

In the present invention, the copper particles that become the core may be particles of various shapes, and may be any one selected from the group consisting of spherical shape, plate shape, dendrite shape, or a combination thereof. Copper particles used in various industrial fields may be spherical, plate-shaped, dendrite-shaped, etc. depending on the field of application, and may be used by mixing them together. Meanwhile, when the size of these particles is analyzed with a laser scattering type particle size analyzer, D ₅₀ may range from 0.1 to 100㎛, where D ₅₀ refers to the particle size when the cumulative percentage of particles reaches 50%. . Based on D ₅₀ , if the particle size of the copper particles is less than 0.1 ㎛, agglomeration between particles is severe, making handling difficult, and forming a surface nickel layer is difficult due to the increased specific surface area. On the other hand, if it exceeds 100 ㎛, the weight of the particles increases, making it difficult to apply them smoothly to electronic components.

In the present invention, the first layer containing silver oxide may further include tin. Tin is an element used to induce silver oxide to smoothly adhere to the surface of copper particles, and when coating in an aqueous solution, copper of the silver element is used. It helps the adhesion to the particle surface. This 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 containing silver oxide may further include metallic silver along with the silver oxide. If metallic silver is further included, the bond with nickel, a metal included in the second layer, can be strengthened. Silver oxide strengthens the bond with copper, and metallic silver bonds strongly with silver oxide and at the same time provides a strong bond with nickel, which is the same metal, thereby further strengthening the bond between the second layer containing nickel and the copper particles. do.

At this time, the molar ratio of the silver element in the silver oxide to the silver element in the metallic ^silver in the first layer ( ^Ag

As described above, containing metallic silver strengthens the bond between the first layer containing silver oxide and the second layer containing nickel, but if the ratio of the silver element in the metallic silver is too high compared to the silver element in the silver oxide, This is undesirable because the bonding force of the first layer with the surface of the copper particles through 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. This molar ratio can be measured using X-ray Photoelectron Spectroscopy (XPS).

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

Additionally, the content of silver included in the first layer may be 10 to 1,000 ppm based on the total weight of the multilayer structure copper particles.

This is because the amount of metallic silver or silver oxide formed in the first layer must be above a certain amount to provide satisfactory bonding strength to the second layer, and too much is undesirable because the process cost increases. More preferably, it may be 10 to 500 ppm.

Additionally, in the present invention, the first layer may be in the form of an island discontinuously formed on the surface of the copper particle. The first layer is a layer that strengthens the bonding force with the core copper particles of the second layer, which provides oxidation resistance, and can sufficiently provide bonding force 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. Even in the case of a continuous film, the particle surface area must be at least 50% or more to provide sufficient bonding force to the second layer.

A second layer containing nickel, a metal with excellent oxidation resistance, is formed on the first layer containing silver oxide. Because nickel has excellent oxidation resistance and chemical resistance while also having 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 contain phosphorus in addition to nickel. The inclusion of phosphorus slightly lowers the electrical conductivity, but improves chemical resistance and oxidation resistance, so when used in parts where reliability is important, It is desirable to include phosphorus along with nickel in the second layer. When phosphorus is included, the phosphorus content 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 will not be achieved, and if phosphorus is included in excess of 13% by weight, sufficient electrical power will not be achieved. This is because conductivity cannot be obtained.

Meanwhile, in terms of electrical conductivity, a low phosphorus content is advantageous, so in fields where electrical conductivity is important, the phosphorus content in the nickel layer is preferably 0.1 to 6% by weight.

In addition, in the present invention, a multi-layer structure of copper particles comprising (a) a first layer forming step of coating silver oxide on the surface of the copper particle, and (b) a second layer forming step 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 can be coated together with the silver oxide. Tin can increase the bonding strength of silver oxide on the surface of copper particles.

Additionally, for more precise control, a tin layer may first be 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 achieved in an alkaline aqueous solution of pH 8 or higher. This is because silver oxide is easily formed in an alkaline atmosphere of pH 8 or higher. More preferably, it can be done in an aqueous solution with a pH ranging from 8 to 10.

In addition, in the method for producing copper particles with a multi-layer structure, after step (a) and before step (b), the copper particles on which the first layer containing the silver oxide is formed are stirred in an aqueous solution with a pH of 8 to 11 and a temperature of 20 to 80 ° C. A post-processing step of controlling the amount of silver oxide may be further included.

When forming the first layer in an aqueous solution, silver ions in the aqueous solution may be reduced and attached to the surface of the copper particles as metallic silver rather than silver oxide. If the ratio of metallic silver becomes too high, it is undesirable because the bonding strength with the copper particles and the second layer may be lowered. Therefore, the amount of silver oxide can be controlled by treatment in an aqueous alkaline solution at an appropriate temperature to increase the content of silver oxide to a desired level.

After controlling the amount of silver oxide in this way, a second layer containing nickel with excellent oxidation resistance is formed, thereby providing conductivity and providing copper particles with a highly reliable multilayer structure.

Forms for practicing the invention

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

The description will be made with reference to the drawings.

The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the examples below may be modified in various other forms, and the scope of the present invention is limited. It is not limited to the examples below. Rather, these embodiments are provided to make the disclosure more faithful and complete and to fully convey the spirit of the invention to those skilled in the art.

[Example 1]

20 g of degreaser (product name: A-screen, Okuno Chemical, Japan) was added to 100 g of deionized water, and the temperature was raised to 60°C. Here, 20 g of spherical copper particles with a D ₅₀ of 20 ㎛ were added and stirred for 30 minutes to remove organic substances and impurities attached to the surface of the copper particles. Afterwards, the copper particles were recovered, stirred in 100 g of deionized water, washed three times, and then 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, washed three times by stirring in 200 g of deionized water, and then recovered. A portion of the powder with the silver oxide layer formed was collected and surface analysis was performed using 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 300g of deionized water solution, 20g of nickel chloride (NiCl ₂ 6H ₂ O), 10g of sodium acetate, 5g of maleic acid, 30g 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 containing mL, stirred, and electroless plating was performed at 70-90°C for 2 hours.

[Example 2]

Pretreatment to remove organic substances 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 of 1.5 g of stannous chloride (SnCl ₂ ·2H ₂ O) and 1 ml of hydrochloric acid (HCl 35% solution) dissolved in 100 g of deionized water and stirring for 30 minutes. The temperature of the aqueous solution was maintained at 35°C. Thereafter, the formation of the first layer containing silver oxide and the second layer containing nickel was performed in the same manner as in Example 1.

[Example 3]

Pretreatment and first layer formation were carried out in the same manner as in Example 1. Afterwards, the nickel layer was formed by adding 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 as a reducing agent, and 10 g of Hydrazine in 300 g of deionized water solution. , the powder formed up to the silver oxide layer was added to a nickel plating solution containing 1 ml of lead acetate, stirred, and electroless plating was performed at 40-60°C for 1 hour.

[Comparative Example 1]

Copper particles were pretreated in the same manner as in Example 1. Afterwards, electroless plating was performed immediately 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 Example 1, a first layer containing silver oxide was formed on the surface of the copper particle. Afterwards, ascorbic acid was added to the aqueous solution to change the 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 forming the first layer of the multi-layered copper particles created in this way, analysis of the silver element ratio 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 conducted. The silver element ratio was analyzed through XPS by collecting samples after forming the first layer. Nickel content and phosphorus content were analyzed using an inductively coupled plasma mass spectrometer (ICP).

Reliability was determined through a reflow test in which a certain amount of copper particles made through examples and comparative examples were mixed with an acrylic binder, applied on a polyimide film, dried, held on molten lead for 30 seconds, and then the conductivity was measured. evaluated.

The results are shown in Table 1 below. Here, the nickel content represents the weight percent of 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 in weight percent.

Ag ^x+ /Ag ⁰ Ni content (wt%) P content (wt%) Coating status 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

Figure 1 shows a scanning electron micrograph of a multilayer-structured copper particle according to an example. Figures 1(a) and (b) are scanning electron microscope images of samples according to Example 1 and Example 2, respectively, and Figures 1(c) and (d) are scanning electron microscope images of samples according to Comparative Example 1 and Comparative Example 2. This is an electron microscope image.

The samples according to Examples 1 and 2 all showed that a dense coating layer was formed, but in the case of Comparative Example 1 without an intermediate silver oxide layer, a poor nickel layer was formed. In addition, when the first layer containing mostly silver metal was formed, the nickel layer was formed stably, but a pinhole was seen in the middle.

Figure 2 shows the results of measuring the ratio of silver elements between silver oxide and metallic silver in the first layer in the sample according to Example 21. As a result of XPS, the ratio of silver in the reduced state and the ratio of silver in the oxidized state can be measured through the peak ratio. Their molar ratio (Ag ^x+ /Ag ⁰ ) in Example 1 was 92.4.

Meanwhile, as shown in Table 1, corrosion resistance was evaluated through a reflow test. In Examples 1 to 3, the resistance of the film using multilayer copper particles was good even after the reflow test, but in Comparative Examples 1 and 2, the coating layer formation was unstable. The resistance increased significantly, and in a film using ordinary copper particles without a protective layer, the resistance was so high that measurement was impossible.

Claims (9)

a first layer comprising silver oxide formed on the surface of the copper particles,
Copper particles having a multilayer structure, comprising a second layer comprising nickel and formed over the first layer. According to claim 1,
The shape of the copper particles is one selected from the group consisting of spherical shape, plate shape, dendrite shape, or a combination thereof, and the particle size of the copper particles is D ₅₀ of 0.1 to 100 when analyzed with a laser scattering type particle size analyzer. Copper particles with a multilayer structure in the ㎛ range. According to claim 1,
The first layer further comprises 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)) is in the range of 10 to 100. Copper particles in the structure. According to claim 1,
Copper particles with a multilayer structure, wherein the first layer further includes tin. According to claim 1,
The content of silver contained in the first layer is 10 to 1,000 ppm of the total weight of the oxidation-resistant copper particles. According to claim 1,
The second layer further includes phosphorus along with the nickel. According to claim 6,
Copper particles with a multilayer structure, wherein the phosphorus in the second layer is 0.1 to 13% by weight. (a) forming a first layer of coating silver oxide on the surface of the copper particles; and
(b) electroless plating nickel on the first layer to form a second layer containing nickel. According to claim 8,
A method for producing copper particles with a multilayer structure, further comprising forming a tin layer before step (a).

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