KR20190080609A - Electroless Ag plating solution and methods of plating using the same - Google Patents

Abstract

The present invention provides an electroless silver plating solution which comprises: silver cyanide as silver salt; at least one selected from sodium cyanide and potassium cyanide as a complexing agent; and any one selected from sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate as a reducing agent.

Description

[0001] Electroless silver plating solution and methods [0002]

The present invention relates to an electroless plating solution and a plating method, and more particularly, to electroless plating solution and a plating method.

Electroless silver plating is a plating that forms a silver plating layer without using an external power source. Electroless silver plating can be roughly classified into reduction plating and substitution plating. In the case of reduction plating, the industrial use is limited due to unstable bathing, and the substitution reaction does not contain a reducing agent, And has a limit to corrosion of the underlying metal as the reaction progresses. Since electroless substitution plating has a limited plating thickness due to the nature of substitution plating, it follows that it follows the shape of the base metal, and it is difficult to make the surface shape different from the base surface through plating. This difficulty of changing the surface shape limits the application of various applications.

1. Korean Patent Publication No. 20170018228 2. Korean Patent Publication No. 20030015226

An object of the present invention is to provide an electroless plating solution and a plating method which can be applied to various applications by adjusting the plating surface according to the type of cyanide to be added. However, these problems are exemplary and do not limit the scope of the present invention.

According to an aspect of the present invention, an electroless plating solution is provided. The electroless silver plating solution is a silver salt; silver cyanide; At least one selected from the group consisting of sodium cyanide and potassium cyanide as complexing agents; And any one selected from among sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate as a reducing agent.

In the electroless silver plating solution, the complexing agent may be composed solely of sodium cyanide to smooth the surface of the silver plating layer to be plated.

In the electroless silver plating solution, the complexing agent may be composed only of potassium cyanide so as to make the surface of the silver plating layer to be plated rugged.

In the electroless silver plating solution, the complexing agent may include both sodium cyanide and potassium cyanide.

In the electroless silver plating solution, when the surface roughness of the silver plating layer plated when the complexing agent is composed only of sodium cyanide is used as a first reference, the surface roughness of the silver plating layer to be plated is relatively more uneven The greater the amount of potassium cyanide in the complexing agent.

In the electroless silver plating solution, when the crystal grain size of the silver plating layer to be plated when the complexing agent is composed only of sodium cyanide is set as the second reference, the larger the grain size of the silver plating layer to be plated is, And relatively more potassium cyanide among the complexing agents.

Wherein the silver salt has a concentration of 1 to 30 g / L in the whole plating solution, the complexing agent has a concentration of 8 to 50 g / L in the whole plating solution, It can have a concentration of 15 g / L.

The electroless silver plating solution may further include at least one selected from ethylenediamine tetraacetic acid and ethylenediamine as a secondary complexing agent.

According to another aspect of the present invention, there is provided a plating method for electroless plating. The electroless silver plating method is silver silver cyanide; At least one selected from the group consisting of sodium cyanide and potassium cyanide as complexing agents; And a reducing agent selected from the group consisting of sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate; And forming an electroless silver plated layer on the metal powder using the electroless silver plating solution.

In the electroless silver plating method, the complexing agent may be composed solely of sodium cyanide so as to smooth the surface of the silver plating layer to be plated.

In the electroless silver plating method, the complexing agent may be composed only of potassium cyanide so as to make the surface of the silver plating layer to be plated rugged.

In the electroless silver plating method, when the surface roughness of the silver plating layer plated when the complexing agent is composed only of sodium cyanide is included as the first reference, the complexing agent includes both sodium cyanide and potassium cyanide, The more rough the surface roughness of the plating layer relative to the first reference, the more the potassium cyanide can be contained in the complexing agent.

In the electroless silver plating method, the complexing agent includes both sodium cyanide and potassium cyanide, and when the complexing agent is composed only of sodium cyanide, when the grain size of the silver plating layer plated is used as the second reference, The greater the grain size of the plated layer relative to the second criterion, the greater the amount of potassium cyanide in the complexing agent.

The electroless silver plating method comprising the steps of: forming an electroless silver plating layer on the metal powder using the electroless silver plating liquid; And removing the oxide film of the metal powder through the pickling process.

According to one embodiment of the present invention as described above, the electroless plating solution and plating method applicable to various applications can be realized by adjusting the plating surface according to the type of cyanide to be added. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating an electroless plating method according to an embodiment of the present invention.
FIGS. 2 to 4 are FE-SEM images showing the surface morphology of the silver plating layer on the metal powder according to the increase of the potassium cyanide addition ratio in the electroless silver plating solution and the plating method according to the experimental example of the present invention.
FIGS. 5 to 6 are photographs of FIB cross section analysis of the uniformity of the thickness of the silver plating layer on the metal powder according to the composition of the complexing agent in the electroless silver plating solution and the electroless plating solution according to the experimental example of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, at least some of the components may be exaggerated or reduced in size for convenience of explanation. Like numbers refer to like elements throughout the drawings.

1 is a flowchart illustrating an electroless plating method according to an embodiment of the present invention.

Referring to FIG. 1, an electroless silver plating method according to an embodiment of the present invention includes the steps of: At least one selected from the group consisting of sodium cyanide and potassium cyanide as complexing agents; And a reducing agent selected from the group consisting of sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate; (S100) preparing an electroless silver plating solution; And a step (S200) of forming an electroless silver plated layer on the metal powder using the electroless silver plating solution. This electroless plating method can control the surface morphology of the plated layer to be plated according to the type of cyanide added to the plating solution. The electroless silver plating method may further include a step (S150) of removing an oxide film of the metal powder through a pickling process between a step S100 and a step S200.

Generally, cyanide in silver salt is more stable than silver nitrate, but silver cyanide is not soluble in water. In the present invention, electroless plating makes it possible to use cyanide silver by adding cyanide as a complexing agent to the plating liquid to form silver complexes. When cyanide is added to the electroless silver plating bath solution, cyanide forms a silver complex, thereby enhancing the stability of the dry bath solution. The stability of the silver ion is increased due to the complex formation, which makes it possible to prevent the silver precipitation and the bath decomposition.

When sodium cyanide (NaCN) is applied as the cyanide, the crystal grain size of the plating layer is small and the surface is formed smooth. On the other hand, when potassium cyanide (KCN) is used as the cyanide, the crystal grain size of the plated layer may be large and the surface may be formed in the shape of a rugged protrusion.

That is, in the electroless silver plating solution and the plating method, the complexing agent may be composed solely of sodium cyanide so as to smooth the surface of the silver plating layer to be plated.

Meanwhile, in the electroless silver plating solution and the plating method, the complexing agent may be composed only of potassium cyanide so as to make the surface of the silver plating layer to be plated rugged.

In addition, the surface roughness and the grain size of the plating layer can be adjusted by appropriately adjusting the amount of sodium cyanide and potassium cyanide simultaneously. That is, when the complexing agent includes both sodium cyanide and potassium cyanide and the complexing agent is composed only of sodium cyanide, when the surface roughness of the silver plating layer to be plated is used as a first reference, the surface roughness of the silver plating layer to be plated is The more irregular the first criterion is, the more the potassium cyanide can be contained in the complexing agent. When the complexing agent is composed of sodium cyanide and potassium cyanide and the complexing agent is composed only of sodium cyanide, when the grain size of the silver plating layer is the second standard, the grain size of the silver plating layer to be plated is The greater the relative value of the second criterion, the greater the amount of potassium cyanide in the complexing agent.

According to another aspect of the present invention, in the electroless plating solution and the plating method, a rugged surface is formed as the ratio of potassium cyanide in the complexed cyanide of the plating bath solution increases, Lt; / RTI > Of course, plating is possible even if only one complexing agent of sodium cyanide and potassium cyanide is added. It can be understood that 10 to 1000 ridges exist for one metal particle in the form of protrusions due to the introduction of complex cyanide. Each ridge may have a diameter ranging from 200 nm to 2 탆. The higher the ratio of potassium cyanide (KCN) in the complexing agent is, the more the bulging point protrudes and the more the number of bulge points increases.

Depending on the type of cyanide added, it can be applied to various applications by adjusting the plating surface. For example, when a rubber socket is manufactured, if the metal powder is plated so as to have a protrusion shape, the pores between the metal powder in the socket are minimized and the contact area is enlarged, thereby improving the electrical conductivity Can be expected. In another example, when it is desired to minimize the voids for improving the electrical conductivity or the thermal conductivity, it is possible to maximize the contact between the metal powders by plating the metal powders so as to have projections. As another example, when the paste is used as filler particles after smooth plating on a spherical metal powder, the ratio of the surface area per volume can be lowered to minimize the increase in the resin viscosity due to the addition of the metal filler particles .

On the other hand, depending on the type of the cyanide to be added, it is possible to control the reflectance and the color by controlling the surface roughness of the metal powder surface by adjusting the surface of the plating. For example, if color is important in finished products that are coated with plated powder, it is possible to adjust reflectivity and color by adjusting the surface roughness of the metal powder surface. As a concrete example, as the surface of the plating layer becomes uneven by increasing the KCN charging ratio, the reflectance decreases and the color becomes dark.

Wherein the silver salt has a concentration of 1 to 30 g / L in the whole plating solution, the complexing agent has a concentration of 8 to 50 g / L in the whole plating solution, It can have a concentration of 15 g / L.

In detail, when a metal powder (metal particle) having an average particle diameter of 1 to 70 μm is plated, since the surface area is very large for the same mass as compared with general bulk plating, silver of the same thickness is plated A large amount of silver salt is needed to do this. The concentration of silver salt in the plating solution is generally from 1 to 20 g / L, depending on the target thickness to be plated. However, in the case of plating silver particles having a small thickness to a large thickness, silver salt of 7 to 30 g / L may be required have. On the other hand, the amount of cyanide complexing agent to be added is 8 to 50 g / L, which is larger than that of general bulk plating.

On the other hand, a supplementary complexing agent may be further included to prevent decomposition of the plating solution due to a high silver salt concentration in the dry bath solution and to enhance stability. The electroless plating solution and the plating method according to an embodiment of the present invention may include ethylene diamine tetraacetic acid or ethylenediamine as the auxiliary complexing agent.

According to a further embodiment of the present invention, the surface of the silver plating layer having the surface morphology controlled by the complex cyanide composition ratio may be further coated with gold, rhodium or palladium.

The electroless plating solution and the electroless plating plating method according to one embodiment of the present invention described above have been described. This technical idea may be implemented in a plating apparatus that performs plating using the plating liquid. In this case, the plating apparatus may further include at least one plating vessel capable of receiving the plating liquid, And a controller capable of adjusting the composition of the complexing agent in the plating liquid so as to be changed in accordance with a required condition.

The controller may be configured to control the complexing agent in the plating liquid to include at least one selected from sodium cyanide and potassium cyanide, and to control the composition ratio in the complexing agent according to the application application required.

For example, the controller can adjust the complexing agent to consist solely of sodium cyanide to smooth the surface of the silver plated layer to be plated, so that the complexing agent is composed solely of potassium cyanide to make the surface of the silver plated layer to be plated rugged Can be adjusted.

In addition, the controller can control the complexing agent to include both sodium cyanide and potassium cyanide. When the complexing agent is composed only of sodium cyanide, when the surface roughness of the silver plating layer to be plated is used as a first reference, The more uneven the surface roughness of the plating layer than the first reference, the more control can be made to include the potassium cyanide in the complexing agent.

The controller may control the complexing agent to include both sodium cyanide and potassium cyanide. When the complexing agent is composed only of sodium cyanide and the crystal grain size of the silver plating layer is the second reference, Can control the relative amount of potassium cyanide in the complexing agent to be larger as the crystal grain size of the plating layer is relatively larger than the second criterion.

Experimental Example

Hereinafter, preferred examples of the present invention will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

FIGS. 2 to 4 are FE-SEM images showing the surface morphology of the silver plating layer on the metal powder according to the increase of the potassium cyanide addition ratio in the electroless silver plating solution and the plating method according to the experimental example of the present invention. Specifically, FIG. 2 corresponds to the case where a plating solution composed only of sodium cyanide is used as a complexing agent, FIG. 3 corresponds to a case where a plating solution composed of sodium cyanide and potassium cyanide in a ratio of 50:50 as a complexing agent is applied, This corresponds to the case where a plating solution composed of only potassium cyanide is applied. As a result, the surface of the plating layer formed by applying the plating solution composed only of sodium cyanide as a complexing agent is smooth, while the surface of the plating layer gradually becomes rugged as the ratio of potassium cyanide in the complexing agent increases.

FIGS. 5 to 6 are photographs of FIB cross section analysis of the uniformity of the thickness of the silver plating layer on the metal powder according to the composition of the complexing agent in the electroless silver plating solution and the electroless plating solution according to the experimental example of the present invention. Specifically, FIG. 5 corresponds to the case where sodium cyanide and potassium cyanide are introduced as a complexing agent, and FIG. 6 corresponds to a case where only sodium cyanide is introduced as a complexing agent. The lower layer in the photograph is a coating material for FIB analysis, and nickel powder, a silver plating layer whose surface shape is adjusted, and a gold plating layer on the silver plating layer are sequentially formed thereon. When sodium cyanide and potassium cyanide are added as a complexing agent, the thickness of the plating layer is relatively uneven from 714 nm to 1083 nm, whereas when only sodium cyanide is introduced as a complexing agent, the thickness of the plating layer is relatively uniform from 927 nm to 991 nm . From this, it can be proved that the surface shape adjustment was made in the silver plating step.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (14)

Silver silver cyanide;
At least one selected from the group consisting of sodium cyanide and potassium cyanide as complexing agents; And
As the reducing agent, any one selected from sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate;
Wherein the electroless silver plating solution is a plating solution. The method according to claim 1,
Characterized in that the complexing agent is composed only of sodium cyanide so as to smooth the surface of the silver plated layer to be plated.
Electroless silver plating solution. The method according to claim 1,
Characterized in that the complexing agent is composed only of potassium cyanide so as to make the surface of the silver plated layer to be plated rugged.
Electroless silver plating solution. The method according to claim 1,
Wherein the complexing agent is sodium cyanide and potassium cyanide.
Electroless silver plating solution. 5. The method of claim 4,
When the complexing agent is composed only of sodium cyanide and the surface roughness of the plated silver layer is the first reference,
Characterized in that the more rough the surface roughness of the silver plating layer to be plated than the first reference, the more the potassium cyanide is contained in the complexing agent.
Electroless silver plating solution. 5. The method of claim 4,
When the complexing agent is composed only of sodium cyanide and the grain size of the plated silver layer is the second reference,
Characterized in that the greater the grain size of the silver plated layer to be plated than the second criterion, the more the potassium cyanide is contained in the complexing agent.
Electroless silver plating solution. The method according to claim 1,
The silver salt has a concentration of 1 to 30 g / L in the whole plating solution,
The complexing agent has a concentration of 8 to 50 g / L in the whole plating solution,
Wherein the reducing agent has a concentration of 10 to 15 g / L in the whole plating solution,
Electroless silver plating solution. The method according to claim 1,
Further comprising at least one selected from ethylenediamine tetraacetic acid and ethylenediamine as the auxiliary complexing agent,
Electroless silver plating solution. Silver silver cyanide; At least one selected from the group consisting of sodium cyanide and potassium cyanide as complexing agents; And a reducing agent selected from the group consisting of sodium potassium tartrate, sodium borohydride, dimethylamine borane, hydrazine, and hydrazine sulfate;
Forming an electroless silver plated layer on the metal powder using the electroless silver plating solution;
/ RTI >
Electroless silver plating method. 10. The method of claim 9,
Characterized in that the complexing agent is composed only of sodium cyanide so as to smooth the surface of the silver plated layer to be plated.
Electroless silver plating method. 10. The method of claim 9,
Characterized in that the complexing agent is composed only of potassium cyanide so as to make the surface of the silver plated layer to be plated rugged.
Electroless silver plating method. 10. The method of claim 9,
The complexing agent includes both sodium cyanide and potassium cyanide,
When the surface roughness of the silver plated layer to be plated when the complexing agent is composed only of sodium cyanide is set as a first reference, the surface roughness of the silver plated layer to be plated becomes relatively more unstable than the first reference, Lt; RTI ID = 0.0 > of: < / RTI >
Electroless silver plating method. 10. The method of claim 9,
The complexing agent includes both sodium cyanide and potassium cyanide,
When the grain size of the silver plating layer to be plated when the complexing agent is composed only of sodium cyanide is set as the second criterion, the larger the grain size of the silver plating layer to be plated is, ≪ RTI ID = 0.0 > more < / RTI >
Electroless silver plating method. 10. The method of claim 9,
Forming an electroless silver plated layer on the metal powder using the electroless silver plating solution; Removing the oxide film of the metal powder through the pickling process,
Electroless silver plating method.

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