KR20090068879A - Electroconductive paste and conductor - Google Patents

Abstract

An electroconductive paste is provided to lower a firing temperature by using the nano-size silver particles, to improve electroconductivity by using nano particle aggregate, and to ensure excellent calcination property. An electroconductive paste comprises silver powder. The Ag powder is silver aggregate(20) formed with the nanosilver particle(10). The silver aggregate is monodispersion. The silver aggregate is sphere and has particle size of 1~2 micron. The average particle size of the nanosilver particle observed on the surface of the aggregate is within 1~300 nm.

Description

Electroconductive Paste And Conductor

The present invention relates to electroconductive pastes and conductors.

A common conductive paste is a silver paste prepared by mixing silver powder and glass frit in an organic vehicle and kneading them.

Recently, the use of electroconductive pastes as internal electrodes of many electronic components has been expanded. The use of the conductive paste has the advantage of being more economical and easier to process than the conventional deposition method, but it is difficult to cope with the high-definition pattern and has to be fired at a high temperature of 500 ° C. or higher for sufficient electrical conductivity. Industrial development has required high-precision and low-temperature firing of conductive pastes. Accordingly, the particle size of silver powder required for silver paste is required to be submicron in size. Manufacturing became possible.

On the other hand, since the nanoparticles have a large specific surface area and high chemical potential, even if the same material is used, the calcinable temperature is lowered only by the effect of particle size. Therefore, the development of low-temperature firing paste utilizing the property of nanoparticles is active. However, another method of securing electrical conductivity remains in the method of lowering the firing temperature using silver nanoparticles. In general, the electrical resistance is inversely proportional to the particle size of the conductor. Conductors made of nanoscale in average particle size have higher resistance than conductors made of micro size. This is because there is a break in the conduction path at the interface between particles and there is a rise in resistance.

For this reason, studies have been conducted to change the shape of the powder for the purpose of improving the electrical properties of the powder. Attempts have been made to ensure flake type particles having a low oxidation rate with a relatively small specific surface area and surface energy, thereby ensuring conductivity with a low coating thickness. However, there is a disadvantage in that proper paste properties appear only through predetermined mixing with spherical particles.

In addition, in the process of forming an electrode and a conductive wire using an electrically conductive paste, dispensing, screen printing, slot coating, roll coating, offset, gravure, etc. do not provide sufficient filling force between the conductive particles constituting the paste. After the paste is formed by simple contact between the particles, the firing causes the grain growth and the breakage of the interparticle contact. Even if nanoparticles are not used, there is no sufficient filling, and as the sintering proceeds, the grain growth is reduced between the grains, resulting in an increase in the resistance of the electric conduction and a decrease in the mechanical strength of the electrode and the lead. Therefore, there is a need for increasing the plasticity after conductor formation.

As a method for solving the above problem, in order to lower the firing temperature of the existing silver paste, it is possible to consider lowering the firing temperature by activating the surface by coating nano-sized silver particles on the surface of the micron-sized silver particles. However, sintering is in the form of inducing bonding between the micron-sized particles through the nanoparticles on the surface, there is a disadvantage that additional coating process of the nanoparticles is required.

In addition, in order to increase the electrical conductivity of the silver paste, a method of improving the plasticity by increasing the filling rate by mixing the nano-sized particles and the micron-sized particles by mixing the bimodal distribution may be considered. There is a disadvantage in that this is required, the practicality is poor.

An object of the present invention is to increase the plasticity of the nanoparticles to effectively solve the problem of electrical conductivity, and at the same time present a form of silver nanoparticle raw material powder that can lower the firing temperature, low firing through the paste using the nanoparticles It is to provide a conductor formed at a temperature.

As a means for achieving the above object,

The present invention provides an electroconductive paste comprising silver powder, wherein the silver powder is a silver aggregate formed by aggregation of silver nanoparticles.

In addition, the aggregate provides an electroconductive paste, characterized in that the monodisperse.

In addition, the silver aggregate is spherical, provides an electroconductive paste, characterized in that the particle size is in the range of 1 ~ 2㎛.

In addition, the average particle size of the silver nanoparticles observed on the surface of the silver aggregate provides an electrically conductive paste, characterized in that in the range of 1 ~ 300nm.

In addition, the inside of the silver aggregate provides an electroconductive paste, characterized in that the boundary of the silver nanoparticles is composed of a large particle, or partially borderless.

The present invention also provides a conductor produced by forming and firing a conductive wire using the aforementioned electroconductive paste, wherein the conductor has a specific resistance value in the range of 3 to 20 µΩ · cm.

In addition, the firing provides a conductor, characterized in that carried out at a low temperature of 250 ~ 400 ℃.

Hereinafter, the present invention will be described in detail.

The electroconductive paste of the present invention is an electroconductive paste comprising silver powder, wherein the silver powder is a silver aggregate formed by aggregation of silver nanoparticles. Preferably it is a silver aggregate formed in the shape of a sphere in the range of 1 ~ 2㎛. Since the silver is composed of agglomerate, it provides an effect of improving both electrical conductivity and plasticity.

1 is a schematic diagram of formation of a silver aggregate 20 according to an embodiment of the present invention. As shown, when silver nanoparticles 10 are aggregated to form a silver aggregate 20, the inside of the aggregate 20 is formed. Firing occurs faster than firing between the aggregates 20 due to the difference in interface area. As the grain grows, the number of particles in the aggregate decreases, and the grain-to-volume ratio decreases. This phenomenon serves to increase the electrical conductivity of the aggregates.

In addition, the plastic behavior between the aggregate 20 and the aggregate 20 can be explained by the existing two-particle model [R. L. Coble, J. Appl. Phys., 32, p.789, 1961], since the size of the contacted particles is smaller than the size of the aggregate 20, the mass transfer is larger than the value predicted in the two-particle model. Therefore, the sintering between the aggregates 20 has an effect that is promoted due to the nanoparticles in contact.

The aggregate 20 is not limited but may be monodisperse. Monodispersity of the particles or aggregates defined in the present invention means that the standard deviation of the particle size of the particles or aggregates has a value within 15%. By having monodispersity, uniform mixing is possible, and due to the nonuniformity of the particle size, the connection between particles during firing may be incomplete, resulting in poor electrical conductivity.

The average particle size of the silver nanoparticles 10 observed on the surface of the silver aggregate 20 is preferably in the range of 1 to 300 nm, more preferably in the range of 10 to 150 nm. To this end, the shape of the silver nanoparticles 10 may have a size of 300 nm or less, more preferably, 150 nm or less in average particle size.

The inside of the silver aggregate 20 is preferably composed of large particles having a boundary between the silver nanoparticles or partially borderless. When the silver nanoparticles are aggregated to form the aggregate 20, the inside of the aggregate may be formed as one large particle as the silver nanoparticles are fused with each other. In this case, the electrical conductivity of the aggregate is increased, which is preferable. In particular, when the paste is calcined, the agglomeration in the agglomerate is faster than the agglomeration between the agglomerates, and the number of particles in the agglomerates is further reduced due to the fusion between the silver nanoparticles, and the grain size ratio is reduced. Will be added.

The silver aggregate can be prepared by reducing the silver-containing aqueous solution or silver complex salt-containing aqueous solution by depositing silver powder, and in addition to the reducing agent, a base and an ammonium salt for increasing the pH are further added to form the aggregate. The conditions for producing the aggregates can be adjusted. In addition, it is also possible to further add fatty acids, fatty acid salts, surfactants, organometallics and protective colloids as dispersants. Detailed manufacturing method will be described later for a specific embodiment.

The electroconductive paste of the present invention may further add components, generally known as the composition of the paste, together with the silver aggregate. For example, it can paste into the following solvents. Hydroxy solvent: ethanol, propanol, propylene glycol, diethylene glycol, triethylene glycol, etc., ketone solvent: acetone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, etc., ester solvent: ethyl acetate, isopropyl acetate, etc. Ether solvent: tetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether and the like; Acrylic solvent: Methyl methacrylate, methacrylic acid, etc., ethyl cellulose, etc. Acetate solvent: Butyl carbitol acetate, ethyl carbitol acetate, cellosolve acetate, etc. Other solvents: Triglyme, isophorone, butyl carbitol , Ethyl carbitol and the like may be used alone or in combination. The solvent and solvent used in the present invention may be selected by mixing at least one type in consideration of solubility, solid content, viscosity of the resulting paste composition, boiling point and the like. In particular, when using the solvent which has a boiling point of 300 degrees C or less, low-temperature baking of 300 degrees C or less is possible.

In addition, those known as known components of other electroconductive pastes may be further added as necessary, and all are included in the present invention.

The present invention also provides a conductor produced by forming a conductive wire and firing the same using the electroconductive paste, wherein the conductor has a specific resistance value in the range of 3 to 20 µΩ · cm. In particular, the electroconductive paste can be performed at a low temperature of 250 ~ 400 ℃ significantly lower than the conventional high temperature firing of more than 500 ℃ excellent plasticity characteristics.

The conductor may be formed by applying the electroconductive paste in a coating process such as dispensing, screen printing, slot coating, roll coating, offset, gravure, or the like to form a conductor such as an electrode and a conductor of an electronic product. After drying, the formed electrode and the conductive wire are fired at a temperature of 250 to 500 ° C, more preferably 300 to 400 ° C in consideration of the boiling point of the solvent. Especially when using the solvent which has a boiling point of 300 degrees C or less, low-temperature baking of 300 degrees C or less is also possible.

In the present invention, using the nano-size silver particles, the firing temperature of the conventional electroconductive paste was reduced from 500 ° C. to 250 ° C. to 400 ° C., and the inferior conductivity of the conventional nano particle fired body was found in the nano particle aggregate. It was remarkably improved by using and the plasticity property was also excellent.

In addition, the nanoparticle aggregates are easily obtained through the control of the dispersant and the reducing agent in the liquid phase reduction process for producing the nanoparticles. In general, much research and effort are required to obtain monodispersed nanoparticles, but aggregates of nanoparticles are easy to control and can be screened to the desired aggregate size through filtering. Therefore, cost reduction for raw material powder production through inexpensive process can be expected.

Hereinafter, the present invention will be described in more detail with reference to examples and drawings. The following examples are specific examples of the present invention, but the present invention is not limited thereto even though there is a certain or definite expression.

Example 1

Preparation of Silver Aggregates

As a starting material, NaOH of the same mass as AgNO ₃ was added to a 1% by weight AgNO ₃ solution, and then a small amount of NH ₄ OH was added dropwise to prepare a reaction solution of a transparent solution. After preparing a reducing solution by mixing HCHO and H 2 O 2 as a reducing agent in a volume ratio of 1: 3, a reducing solution of 5 vol% of the reaction solution was rapidly added dropwise at room temperature to reduce the reaction to obtain an aggregate. The obtained aggregate was dried and pulverized to obtain a final aggregate having a uniform 1.5 탆 particle size through the filling.

Preparation of Electroconductive Paste and Preparation of Electrode

70 wt% of the silver aggregate and 30 wt% of triethylene glycol were kneaded to prepare a paste, and then, an electrode line pattern was formed by dispensing through a 0.5 mm nozzle and baked at 300 ° C. for 30 minutes to complete the electrode.

Figure 2 is an SEM image of the aggregate of Example 1, it can be seen that the silver particles having an average particle size of 150 nm is agglomerated to disperse the aggregate of about 1.5㎛ size.

3 is a microstructure photograph of an electrode prepared by baking the paste of Example 1. FIG. The aggregate in the embodiment can not determine the shape therein, but can be determined as the aggregate of the nanoparticles in view of the shape on the surface.

300 ℃ is more than half lower than the general firing temperature of 500 ~ 700 ℃, but after firing the microstructure forms a distinct interface between the silver particles, the particle size can be seen to grow to the size of the aggregate. Since sufficient interface was formed between the particles, the growth of the particles was accompanied, and the filling rate is excellent, the effect of electron transfer on the electric conduction on the electric conduction is expected to be low. In fact, the specific resistance measured using four-point-probe was 6.6 mW · cm, which was 4 times higher than that of 1.6 mW · cm, which is known as pure bulk silver. As a result of experiments with various examples, it was found that most of the resistivity values were in the range of 3 to 20 μΩ · cm and the electrical conductivity was good.

Comparative Example 1

In the above examples, the same procedure was conducted except that monodispersed silver powder was used instead of silver aggregates with an average particle size of 150 nm.

FIG. 4 is a SEM photograph of the silver powder of Comparative Example 1, and FIG. 5 is a microstructure photograph of the electrode manufactured by baking with the paste of Comparative Example 1. FIG.

After firing, the microstructure has high porosity, and most of the particles do not grow, and only some of the particles form aggregates and grow large. Since no interface is formed and grain growth is nonuniform, electrical conductivity is expected to be low. The actual measured specific resistance was 132 µΩ · cm, which was about 20 times higher than that of Example 1. In addition, the practical value of the conductor is very low as 80 times higher than that of pure silver.

1 is a schematic diagram of formation of silver aggregates according to an embodiment of the present invention;

2 is a SEM photograph of the aggregate of Example 1 of the present invention,

Figure 3 is a microstructure photograph of the electrode prepared by firing the paste of Example 1 of the present invention,

4 is a SEM photograph of the silver powder of Comparative Example 1;

5 is a microstructure photograph of an electrode prepared by baking with the paste of Comparative Example 1. FIG.

** Description of the major symbols in the drawings **

10: silver nanoparticles

20: silver aggregate

Claims (7)

An electroconductive paste comprising silver powder, The silver powder is an electrically conductive paste is a silver aggregate formed by agglomeration of silver nanoparticles. The electroconductive paste of claim 1, wherein the silver aggregate is monodisperse. The electrically conductive paste of claim 1, wherein the silver aggregate is spherical and has a particle size in a range of 1 to 2 μm. The electroconductive paste of claim 1, wherein the average particle size of the silver nanoparticles observed on the surface of the silver aggregate is in a range of 1 to 300 nm. The electrically conductive paste of claim 1, wherein the inside of the silver agglomerate is composed of large particles having a boundary of the silver nanoparticles or partially bordering. A conductor manufactured by forming and firing a conductive wire using the electroconductive paste of any one of claims 1 to 5, A conductor, characterized in that the resistivity value is in the range of 3 to 20 µΩ · cm. The conductor according to claim 6, wherein the firing is performed at a low temperature of 250 to 400 ° C.

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