Multilayered copper particles with excellent corrosion resistance

Abstract

The present invention aims to provide copper particles having a nickel metal layer formed on the surface thereof, which has excellent electrical conductivity, corrosion resistance, and bonding strength with copper particles. In order to achieve the above-mentioned object, the present invention can provide copper particles having a multilayer structure including a second layer containing nickel formed on the first layer.

Description

[Technical Field]

[0001] The present invention relates to copper particles having a multilayer structure with a nickel coating layer on the surface, and in particular to copper particles having a multilayer structure in which a bonding layer containing silver oxide is first formed on the surface of the copper particles, and then a nickel metal layer with improved density and bonding is formed on the surface, thereby improving electrical conductivity and oxidation resistance, and a method for producing the same. [Background technology]

[0002] Conductive particles are widely used in electronic materials. Copper particles, among others, have high conductivity and are highly cost-competitive, making them widely used in a variety of electronic components, including films, adhesives, and coating slurries, which require electrical conductivity.

[0003] However, these copper particles have high electrical conductivity close to that of silver and are much cheaper than silver, but they have a problem of poor oxidation resistance, which reduces reliability and significantly limits the fields in which copper particles can be applied.

[0004] Therefore, if a protective coating layer with high oxidation resistance and electrical conductivity could be formed on the surface, these problems of low reliability could be solved. Such a protective coating layer is typically made of nickel or silver.

[0005] The key to these coating layers is that pinholes and low density protective coating layers must not be formed, as this can lead to rapid oxidation of the core copper particles.

[0006] Therefore, the important point in copper particles having a protective coating layer is the formation of a dense and defect-free protective coating layer. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide copper particles having a nickel metal layer formed on the surface, which is excellent in electrical conductivity and has an excellent binding force between corrosion resistance and copper particles.

[0008] Still another object of the present invention is to provide a method for producing composite copper particles capable of forming, at a low cost, a nickel metal layer excellent in electrical conductivity and having an excellent binding force between corrosion resistance and copper particles on the surface of copper particles.

Means for Solving the Problems

[0009] In order to achieve the above object, the present invention can provide copper particles having a multilayer structure including a first layer containing silver oxide formed on the surface of the copper particles and a second layer containing nickel formed on the first layer.

[0010] In one embodiment of the present invention, the shape of the copper particles is selected from the group consisting of spherical, plate-like, dendritic, or combinations thereof, and the particle size of the copper particles is D ,

[0013] , , x+ , ,

[0011] , , 0 , , ,

[0012] , ,

[0014] may be in the range of 0.1 to 100 μm when analyzed by a particle size analyzer using the laser scattering method.

[0011] In one embodiment of the present invention, the first layer further contains 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)) may be in the range of 10 to 100.

[0012] In one embodiment of the present invention, the first layer may further contain tin.

[0013] In one embodiment of the present invention, the first layer may include a tin layer formed on the surface of the copper particles and a silver oxide layer formed on the tin layer.

[0014] <_{0000062}In one embodiment of the present invention, the content of silver in the first layer may be 10 to 1,000 ppm based on the total weight of the oxidation-resistant copper particles.

[0015] In one embodiment of the present invention, the first layer may be in the form of discontinuous islands on the surface of the copper particles.

[0016] In one embodiment of the present invention, the second layer may further contain phosphorus together with the nickel, and the phosphorus content in the second layer may be 0.1 to 13 wt %.

[0017] The method for producing multilayered copper particles according to the present invention may include (a) a step of forming a first layer by coating the surface of a copper particle with silver oxide, and (b) a step of electrolessly plating nickel onto the first layer to form a second layer containing nickel.

[0018] Also, in step (a), tin can always be coated together with silver oxide.

[0019] Furthermore, the method may further include a step of forming a tin layer before the step (a). [Effects of the Invention]

[0020] The multilayered copper particles according to the present invention are inexpensive yet have excellent electrical conductivity and corrosion resistance, making them applicable to various electronic components that require electrical conductivity. They also have excellent bonding strength in the surface metal layer, making it possible to reduce the weight of the components to which they are applied and improve their electrical conductivity and reliability.

[0021] Furthermore, the method for producing multilayered copper particles provided by the present invention enables mass production of multilayered copper particles with excellent conductivity and reliability through an inexpensive process. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a scanning electron microscope image of multilayered copper particles according to an embodiment of the present invention and a comparative example. [Figure 2]FIG. 1 is a diagram showing the results of analysis of multilayered copper particles in one example according to the present invention by X-ray Photoelectron Spectroscopy (XPS).

[0023] BEST MODE FOR CARRYING OUT THE INVENTION The following describes the configuration and operation of an embodiment of the present invention with reference to the accompanying drawings. In the following description of the present invention, if a detailed description of a related known function or configuration is deemed to obscure the gist of the present invention, the detailed description will be omitted. Furthermore, when a part "includes" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified.

[0024] Copper particles can be produced in a variety of shapes and sizes. However, due to the material's characteristics, they have very low oxidation resistance, corrosion resistance, and chemical resistance, making it impossible to prevent their electrical conductivity from rapidly deteriorating depending on the usage environment and the passage of time. To overcome this, forming a conductive metal layer on the surface as a protective layer can impart a high level of oxidation resistance to copper particles of various shapes and sizes. Nickel and silver are often used as protective layers, but silver is a precious metal and is therefore expensive, so there have been various attempts to form nickel as a protective layer.

[0025] Meanwhile, when nickel is used as the protective layer, it is important that the nickel protective layer is formed densely without defects such as pinholes, because defects such as pinholes can cause rapid corrosion around these defects.

[0026] For this reason, the present invention can provide copper particles having a multilayer structure including a first layer containing silver oxide formed on the surface of the copper particles, and a second layer containing nickel formed on the first layer.

[0027] The inventors of the present invention have found that forming a binding layer containing silver oxide before forming a nickel protective layer improves the density of the final nickel protective layer and also increases the bonding strength with the copper particles. Based on this finding, rather than forming a nickel protective layer directly on the surface of copper particles, the inventors have been able to develop copper particles with a multilayer structure in which a nickel protective layer is formed densely without pinholes by forming a binding layer containing silver oxide between the surfaces of the copper particles.

[0028] The copper particles serving as the core in the present invention may have various shapes, and may be any one selected from the group consisting of spherical, plate-like, dendritic, and combinations thereof. Copper particles used in various industrial fields may be spherical, plate-like, dendritic, etc., depending on the field of application, and these may also be used in combination. Meanwhile, the size of these particles is determined by the D 50 may be in the range of 0.1 to 100 μm, where D 50 D means the particle size when the cumulative percentage of particles reaches 50%. 50 If the particle size of the copper particles is less than 0.1 μm, excessive aggregation between particles occurs, making them difficult to handle, and the increased specific surface area makes it difficult to form a nickel layer on the surface. 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 components.

[0029] In the present invention, the first layer containing silver oxide may further contain tin, which is an element used to facilitate smooth adhesion of silver oxide to the surface of copper particles and helps silver element adhere to the surface of copper particles when coating is performed with an aqueous solution. The tin may constitute the first layer together with silver oxide, or may be formed between the first layer containing silver oxide and the surface of the copper particles.

[0030] In the present invention, the first layer containing silver oxide may further contain metallic silver together with silver oxide. However, when metallic silver is further contained, the bond with nickel, which is the metal contained in the second layer, can be further strengthened. Silver oxide strengthens the bond with copper, and metallic silver strongly bonds with these silver oxides and provides a strong bond with nickel, which is the same metal. As a result, the bonding force between the second layer containing nickel and copper particles is further strengthened.

[0031] At this time, the molar ratio (Ag x+ / Ag 0 (0 < x ≤ 3)) of silver element in silver oxide to silver element in metallic silver in the first layer is preferably in the range of 10 to 100.

[0032] As described above, containing metallic silver strengthens the bond between the first layer containing silver oxide and the second layer containing nickel. However, if the proportion of silver element in metallic silver is too high compared to the silver element in silver oxide, the bonding force between the surface of the copper particles in the first layer and silver oxide decreases accordingly, which is not preferable. Therefore, the molar ratio of silver element in metallic silver to silver element in silver oxide is preferably 10 to 100 so that the proportion of silver element in silver oxide is higher. These molar ratios can be measured by X-ray Photoelectron Spectroscopy (XPS).

[0033] Here, the oxidation number of silver in silver oxide can be from +1 to +3. In the amorphous phase, the oxidation number does not have to be a constant. Therefore, the oxidation number of silver in silver oxide may be greater than 0 and less than or equal to 3.

[0034] <着 Also, the content of silver contained in the first layer may be 10 to 1,000 ppm of the total weight of the copper particles in the multilayer structure.

[0035] The metallic silver or silver oxide formed in the first layer must have a certain content or more in order to provide a satisfactory level of bonding strength to the second layer, and if the content is too high, the process cost increases, which is undesirable. More preferably, it may be 10 to 500 ppm.

[0036] The first layer in the present invention may be discontinuous islands formed on the surface of the copper particle, and the first layer strengthens the bonding strength between the second layer, which provides oxidation resistance, and the copper particle core, and even if the first layer is discontinuous islands, it can provide sufficient bonding strength to the second layer.

[0037] On the other hand, the first layer may be in the form of a continuous film, in which case it occupies at least 50% or more of the surface area of ​​the copper particles, because even if it is in the form of a continuous film, it must occupy at least 50% or more of the surface area of ​​the particles in order to provide sufficient bonding strength to the second layer.

[0038] A second layer containing nickel, a metal with excellent oxidation resistance, is formed on the first layer containing silver oxide. Nickel has excellent oxidation resistance and chemical resistance, as well as relatively high electrical conductivity, which gives the multilayered copper particle structure excellent electrical conductivity and reliability at the same time.

[0039] These nickel-containing second layers may further contain phosphorus in addition to nickel, but the inclusion of phosphorus slightly reduces electrical conductivity but improves chemical resistance and oxidation resistance, so it is preferable for the second layer to contain phosphorus in addition to nickel when used in parts where reliability is important. If phosphorus is included, the phosphorus content in the second layer is preferably 0.1 to 13.0 wt %, but if it is too low, the desired improvement in chemical resistance and oxidation resistance will not be achieved, and if it contains more than 13 wt %, sufficient electrical conductivity will not be obtained.

[0040] On the other hand, from the viewpoint 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 wt %.

[0041] The present invention also provides a method for producing multilayered copper particles, which includes (a) a step of forming a first layer by coating the surface of a copper particle with silver oxide, and (b) a step of forming a second layer by electrolessly plating nickel on the first layer.

[0042] The surface of the copper particles is coated with a first layer containing silver oxide, which can be coated with tin in addition to the silver oxide. The tin strengthens the bonding strength of the silver oxide on the surface of the copper particles.

[0043] For more precise control, a tin layer can be formed on the surface of the copper particles first, followed by the formation of the first layer containing silver oxide.

[0044] The first layer containing silver oxide can be formed using an alkaline aqueous solution with a pH of 8 or higher. This is because silver oxide is well formed in an alkaline atmosphere with a pH of 8 or higher. More preferably, the first layer can be formed using an aqueous solution with a pH in the range of 8 to 10.

[0045] Furthermore, the method for producing multilayered copper particles may further include, after step (a) and before step (b), a post-treatment step of stirring the copper particles on which the first layer containing silver oxide has been formed in an aqueous solution having a pH of 8 to 11 and a temperature of 20 to 80°C to adjust the amount of silver oxide.

[0046] When the first layer is formed in an aqueous solution, silver ions in the aqueous solution may be reduced and adhere to the surface of the copper particles as metallic silver rather than silver oxide. If the proportion of metallic silver is too high, the bonding strength between the copper particles and the second layer may be weakened, which is undesirable. Therefore, to increase the silver oxide content to the desired level, the amount of silver oxide can be adjusted by treating the copper particles with an alkaline aqueous solution at an appropriate temperature.

[0047] In this way, by adjusting the amount of silver oxide and then forming a second layer containing nickel, which has excellent oxidation resistance, it is possible to impart conductivity and provide copper particles with a highly reliable multilayer structure. DETAILED DESCRIPTION OF THE INVENTION

[0048] In order that the present invention may be fully understood, preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0049] The examples 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 various different forms, and the scope of the present invention is not limited to the following examples. Rather, these examples are provided to make the present disclosure more complete and thorough, and to fully convey the concept of the present invention to those skilled in the art.

[0050] [Example 1] 20 g of a degreasing agent (product name: Ace Clean, manufactured by Okuno Chemical Co., Ltd., Japan) was added to 100 g of deionized water, and the temperature was raised to 60°C. 50 20 g of spherical copper particles with a diameter of 20 μm were added and stirred for 30 minutes to perform pretreatment to remove organic matter and impurities attached to the surface of the copper particles. The copper particles were then collected and washed three times with 100 g of deionized water before being collected.

[0051] The recovered copper particles were added to a silver nitrate solution prepared by dissolving 0.15 g of silver nitrate (AgNO3) in 100 g of deionized water and stirred. At this time, 28% ammonia water was added dropwise to adjust the pH to 9.1.

[0052] The temperature was maintained at 40°C and the mixture was stirred for 1 hour to form a silver oxide layer. After 1 hour, the mixture was filtered and collected, then stirred with 200 g of deionized water and washed three times before being collected. A portion of the powder with the silver oxide layer formed was sampled and subjected to surface analysis by X-ray photoelectron spectroscopy (XPS).

[0053] The powder with the silver oxide layer formed was collected and a nickel coating layer was formed using electroless plating. The powder with the silver oxide layer formed was added to a nickel plating solution composed of 300g of deionized water solution, 20g of nickel chloride (NiCl2·6H2O), 10g of sodium acetate, 5g of maleic acid, 30g of sodium hypophosphite (a reducing agent), and 3ml of lead acetate. The solution was stirred and electroless plating was performed at 70-90°C for 2 hours.

[0054] [Example 2] Pretreatment to remove organic matter and impurities adhering to the surface of the copper particles was performed in the same manner as in Example 1, after which a tin layer was formed. The tin layer was formed by placing the copper particles in an aqueous solution prepared by dissolving 1.5 g of stannous chloride (SnCl2·2H2O) and 1 ml of hydrochloric acid (35% HCl solution) in 100 g of deionized water and stirring for 30 minutes. The temperature of the aqueous solution was maintained at 35°C. Then, a first layer containing silver oxide and a second layer containing nickel were formed in the same manner as in Example 1.

[0055] [Example 3] The pretreatment and formation of the first layer were carried out in the same manner as in Example 1. Thereafter, the nickel layer was formed by adding the powder with the silver oxide layer formed to a nickel plating solution composed of 300 g of deionized water solution, 20 g of nickel chloride (NiCl2·6H2O), 10 g of sodium acetate, 3 g of ammonia water, 10 g of sodium hypophosphite and 10 g of hydrazine as reducing agents, and 1 ml of lead acetate, stirring the solution, and performing electroless plating at 40 to 60°C for 1 hour.

[0056] [Comparative Example 1] Copper particles were pretreated in the same manner as in Example 1. Then, without forming a silver oxide layer, electroless plating was immediately performed to form a second layer containing nickel. The electroless plating of nickel was performed in the same manner as in Example 1.

[0057] Comparative Example 2 As in Example 1, a first layer containing silver oxide was formed on the surface of the copper particles. Then, ascorbic acid was added to the aqueous solution to convert the silver oxide on the surface into metallic silver, and then electroless plating was performed to form a second layer containing nickel. The electroless nickel plating was performed in the same manner as in Example 1.

[0058] After forming the first layer on the multilayered copper particles, the silver content of silver oxide and metallic silver was analyzed, and the nickel and phosphorus contents were analyzed. The coating condition was also observed using a scanning electron microscope (SEM). The silver content was analyzed by XPS on a sample taken after forming the first layer. The nickel and phosphorus contents were analyzed using inductively coupled plasma mass spectrometry (ICP).

[0059] The reliability was evaluated by a reflow test in which copper particles prepared according to the examples and comparative examples were mixed with a certain amount of acrylic binder, coated on a polyimide film, dried, and then placed on molten lead for 30 seconds, after which the conductivity was measured.

[0060] The results are shown in Table 1 below. Here, the nickel content is expressed as the weight % of nickel based on the entire multilayer structure of copper particles, and the phosphorus content is expressed as the content in the second layer containing nickel in weight %.

[0061] [Table 1]

[0062] Figure 1 shows scanning electron microscope images of multilayered copper particles according to the examples. Figures 1(a) and 1(b) are scanning electron microscope images of samples according to Examples 1 and 2, respectively, and Figures 1(c) and 1(d) are scanning electron microscope images of samples according to Comparative Examples 1 and 2.

[0063] Both the samples of Examples 1 and 2 showed the formation of dense coating layers, but in the case of Comparative Example 1, which did not have an intermediate silver oxide layer, it was found that a non-dense nickel layer was formed. Also, when the first layer, which was mostly metallic silver, was formed, it was found that the nickel layer was formed stably, but there were pinholes between them.

[0064] FIG. 2 shows the results of measuring the ratio of silver element between silver oxide and metallic silver in the first layer of the sample of Example 2. As a result of XPS, it can be measured by the ratio of the peaks of the ratio of silver in the reduced state and the ratio of silver in the oxidized state. These molar ratios (Ag x+ / Ag 0 ) was 92.4.

[0065] On the other hand, as shown in Table 1, corrosion resistance was evaluated by a reflow test. In Examples 1 to 3, the resistance of the films using multilayered copper particles was good even after the reflow test, but in Comparative Examples 1 and 2, where the formation of the coating layer was unstable, the resistance increased significantly, and the resistance of the film using ordinary copper particles without a protective layer was too high to be measured.

Claims

1. a first layer including silver oxide formed on the surface of the copper particles; a second layer formed on the first layer and comprising nickel; Including, Multilayered copper particles.

2. The shape of the copper particles is any one selected from the group consisting of spherical, plate-like, dendritic, and combinations thereof, and the particle size of the copper particles is D when analyzed by a laser scattering particle size analyzer. ５０ is in the range of 0.1 to 100 μm, The multilayered copper particles according to claim 1 .

3. The first layer further contains 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; The multilayered copper particles according to claim 1 .

4. the first layer further comprises tin; The multilayered copper particles according to claim 1 .

5. The silver content in the first layer is 10 to 1,000 ppm based on the total weight of the multi-layered copper particles. The multilayered copper particles according to claim 1 .

6. The second layer further contains phosphorus together with the nickel. The multilayered copper particles according to claim 1 .

7. the phosphorus in the second layer is 0.1 to 13 wt %; The multilayered copper particles according to claim 6.

8. (a) forming a first layer by coating silver oxide on the surface of copper particles; (b) electrolessly plating nickel onto the first layer to form a second layer comprising nickel; Including, A method for manufacturing multilayered copper particles.

9. The method further includes forming a tin layer before the step (a). A method for producing the multilayered copper particles according to claim 8.

Images