TW202144623A - Cyanide type electrolytic roughening silver plating liquid - Google Patents

Abstract

The present invention provides an electrolytic silver plating liquid which contains from 10 g/L to 100 g/L of silver cyanide or a silver cyanide salt in terms of elemental silver, from 1 g/L to 200 g/L of an electrically conductive salt, and from 3 g/L to 500 g/L of a thiosulfate or a salt thereof.

Description

Cyanide electrolytic roughening silver plating solution

The present invention relates to electroplating silver baths. Specifically, about the silver electroplating liquid which used silver cyanide as a silver source, the electroplating silver liquid of the coating film which was highly roughened was obtained.

Silver has been used in jewelry products since ancient times due to its white luster. Since silver is relatively cheap among precious metals, silver plating is applied even in modern times for decorative purposes such as silver accessories or tableware. In addition, since silver has the highest electrical conductivity among all metals at room temperature, silver plating is also widely used in lead frames, substrates, and the like of electronic devices such as ICs and transistors. Furthermore, since silver has the highest reflectivity of visible light among all metals, silver plating is often used on lead frames and various substrates for light-emitting devices such as LEDs. In addition, silver plating is also used for bearing parts or applications utilizing the antibacterial properties of silver.

So far, various measures have been taken in the semiconductor industry in order to improve the reliability of IC packages. In particular, in order to prevent the destruction of IC packages called the popcorn phenomenon, rough plating has been developed. The plating surface of copper or nickel used as base plating is roughened, and the aim is to improve the adhesion between plating and resin by the anchor effect. For example, Patent Document 1 describes a technique for improving adhesion by using two-layer roughening plating. However, in these conventional techniques, since only the outermost surface is covered with a noble metal plating layer, there is a problem that the anchoring effect cannot be sufficiently exerted. Therefore, a method of roughening the silver plating itself excellent in electrical properties and applying it to the outermost surface is desired. On the other hand, the silver-plated system has the characteristic of being easily recrystallized by heat. Therefore, in the case of silver plating, the needle-like plating as seen in conventional rough copper plating or rough nickel plating has a possibility of lowering the anchoring effect due to heat treatment.

A silver plating solution using a chalcogenide compound has been conventionally known. Patent Document 2 discloses a silver plating solution containing a thiol or a disulfide compound as a stabilizer for silver in place of cyanide. In addition, Patent Document 3 discloses a method of stabilizing the plating solution by thiosulfuric acid. In this way, a sulfur compound, especially thiosulfuric acid, is used as a stabilizer or a reducing agent in a cyanide-free silver plating solution or an electroless silver plating solution, or the like. However, thiosulfuric acid is also known as an antidote for cyanide compounds, and there is no example of using thiosulfuric acid or its salt in a cyanide electroplating silver bath for the purpose of roughening plating. [Prior Art Literature]

[Patent Document 1] International Publication No. WO2017/077903 [Patent Document 2] Japanese Patent No. 6608597 [Patent Document 3] Japanese Patent No. 3300519

[Problems to be solved by the invention]

In view of the above, in the prior art, it was not easy to improve the adhesion between noble metals, especially silver, which is excellent in electrical properties and solder wettability, and resins. In addition, the needle-shaped silver system has a concern that the performance is lowered due to recrystallization, or that the whisker of the metal single crystal grows spontaneously on the metal surface. Therefore, it is desired to develop a silver plating solution that can obtain a silver film roughened in a non-needle form.

The object of the present invention is to provide a silver electroplating solution which can obtain a highly roughened silver film. [Means to solve the problem]

The inventors of the present invention have made intensive studies and found that by adding thiosulfuric acid and/or its salts to the silver electroplating solution, a non-needle-shaped, highly roughened silver film can be obtained, and the present invention was finally completed. The present invention for solving the above-mentioned problems is described below.

[1] A silver electroplating solution, characterized by containing: Silver cyanide or silver cyanide salt of 10-100g/L converted to silver, 1～200g/L of conductive salt, with 3～500g/L of thiosulfuric acid or its salt.

[2] The silver electroplating solution according to [1], wherein the conductive salt is selected from cyanide, phosphate, pyrophosphate, nitrate, citrate, tartrate, thiocyanate, sulfate and boric acid or its At least one of the group consisting of salt.

[3] The silver electroplating solution according to [1], wherein the pH (25° C.) is 7.0 to 13.0. [Effect of invention]

The electrolytically roughened silver plating solution of the present invention can stably obtain a non-needle-shaped, highly roughened silver film. Specifically, as shown in FIGS. 1 and 2 , a coating in the shape of a massive crystal growth was obtained. Thereby, there is little possibility of deterioration of the roughened shape due to recrystallization. In addition, large unevenness occurs in the direction in which the plating grows, and a high anchoring effect is obtained when it is attached to a resin or the like. Furthermore, since stable performance is obtained, the manufacturing yield is improved.

[The form of carrying out the invention]

The silver electroplating solution of the present invention contains silver cyanide complexes of 10-100 g/L of silver salt, 1-200 g/L of conductive salt and 3-500 g/L of thiosulfuric acid or its salt. Hereinafter, each component which comprises the silver electroplating liquid of this invention is demonstrated.

[Silver cyanide complex] In the silver electroplating solution of the present invention, as the silver source, well-known silver cyanide complexes can be used without limitation. Examples of the silver cyanide complex include silver cyanide, silver potassium cyanide, and silver sodium cyanide.

The concentration of the silver cyanide complex in the silver electroplating solution of the present invention, as the concentration of silver ions, is preferably 10-100 g/L, more preferably 20-70 g/L. When the silver ion concentration is less than 10 g/L, the precipitation efficiency decreases, and the desired silver film thickness may not be obtained. On the other hand, when the silver ion concentration exceeds 100 g/L, the loss of the silver salt due to being carried out of the plating solution by the object to be plated increases, which is uneconomical.

[conductive salt] The conductive salt blended in the silver electroplating solution of the present invention is not particularly concerned as long as the aqueous solution has conductivity, but it is preferable to include At least one selected from cyanide, phosphate, nitrate, citrate, tartrate, thiocyanate, sulfate, and boric acid or its salt. Moreover, a soluble organic acid salt etc. are also preferable. These may be used alone or in combination of two or more. As a cyanide salt, potassium cyanide, sodium cyanide, etc. can be illustrated. As a phosphate, potassium phosphate, sodium phosphate, ammonium phosphate, etc. can be illustrated. As a pyrophosphate, potassium pyrophosphate, sodium pyrophosphate, ammonium pyrophosphate, etc. are illustrated. As nitrate, potassium nitrate, sodium nitrate, ammonium nitrate, etc. are illustrated. As a citrate, potassium citrate, sodium citrate, ammonium citrate, etc. are illustrated. As tartaric acid, potassium tartrate, sodium tartrate, sodium potassium tartrate, etc. can be illustrated. As a thiocyanate, potassium thiocyanate, sodium thiocyanate, etc. can be illustrated. As a sulfate, potassium sulfate, sodium sulfate, ammonium sulfate, etc. can be illustrated. As boric acid or its salt, boric acid, sodium borate, potassium borate, etc. can be illustrated.

The concentration of the conductive salt in the silver electroplating solution of the present invention is preferably 1-200 g/L, more preferably 10-200 g/L, and particularly preferably 20-180 g/L. When the concentration of the conductive salt is less than 1 g/L, the resistance of the plating solution becomes too high, and the plating production cannot be performed with an appropriate cathode current density.

[thiosulfuric acid (salt)] The thiosulfuric acid and/or its salt (hereinafter referred to as "thiosulfuric acid (salt)") blended in the silver electroplating solution of the present invention can be specifically exemplified by thiosulfuric acid, potassium thiosulfate, and sodium thiosulfate Wait. These may be used alone or in combination of two or more.

The concentration of thiosulfuric acid (salt) in the silver electroplating solution of the present invention is preferably 3-500 g/L, more preferably 3-300 g/L, and particularly preferably 3-150 g/L. When the concentration of thiosulfuric acid (salt) is less than 3 g/L, the shape and size of the precipitated silver crystals become uneven. When the concentration of thiosulfuric acid (salt) exceeds 500 g/L, precipitation may occur.

[other ingredients] In the silver electroplating solution of the present invention, in addition to the above-mentioned components, in order to reduce the viscosity and suppress the occurrence of unevenness of the silver film, components such as surfactants may be contained within the range that does not impair the purpose of the present invention. Examples of the surfactant include anionic surfactants such as polyoxyethylene alkyl ether sodium sulfate, and nonionic surfactants such as polyoxyethylene alkyl ether condensates.

The silver electroplating solution of the present invention can be produced by dissolving the above-mentioned silver cyanide or silver cyanide salt, conductive salt, thiosulfuric acid and/or its salt and other components as needed in water. Moreover, it is also preferable to dissolve a conductive salt, thiosulfuric acid and/or its salt, and other components as needed in water in advance, and to add silver cyanide or a silver cyanide salt at the time of use.

The silver electroplating solution of the present invention is preferably used at pH 7.0-13.0 (25° C., the same below), more preferably at pH 8.0-13.0. When the pH is less than 7.0, the cathodic current efficiency decreases, and the obtained film does not form a sufficient film thickness. When the pH exceeds 13.0, the appearance of the obtained film deteriorates.

The liquid temperature of the silver electroplating solution of the present invention is preferably 10-80°C, more preferably 20-60°C. When the liquid temperature of the plating bath deviates from the above-mentioned range, the cathode current efficiency decreases, and the stability of the plating bath may be impaired.

The current density when the silver electroplating solution of the present invention is used is set in consideration of the composition of the plating solution, the solution temperature, and other conditions. For example, when the plating solution is used at a solution temperature of 60° C., the current density is preferably set to 30 to 100 A/dm ² . If the current density is not set to an appropriate current density, there is a possibility of abnormality in the appearance of the plating and the properties of the plating film. In addition, the plating bath becomes unstable, and decomposition of the plating solution components may occur. [Example]

Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited by these embodiments.

(Examples 1 to 12 and Comparative Examples 1 to 7) As the object to be plated, a 0.1 dm ² copper plate was used. First, the copper plate was subjected to degreasing treatment with an alkali-based degreasing solution, neutralized with dilute sulfuric acid, and then subjected to matt copper plating of about 1.7 μm in a cyanide bath. Then, silver plating of about 0.1 μm was applied by a cyano-based primer bath.

With the compositions described in Tables 1 and 2, the plating solutions of Examples 1 to 12 and Comparative Examples 1 to 7 were prepared. Spray 0.5L of the prepared plating solution with a pump, and spray the plating solution to the object to be plated that remains in a square of 1 cm square and has been masked. The thickness was 4 μm, washed with clean pure water, and dried.

The glossiness and the arithmetic mean roughness of the silver films of Examples 1 to 12 and Comparative Examples 1 to 7 obtained as described above were measured. The glossiness mentioned here is the value measured by the optical density meter ND-11 made by Nippon Denshoku Kogyo Co., Ltd. In addition, the arithmetic mean roughness referred to here is the value of the arithmetic mean roughness obtained by analysis at a magnification of 150 times using a shape measuring laser microscope VK-9700 manufactured by KEYENCE Co., Ltd. The measurement results are shown in Tables 1 and 2.

Moreover, the silver films of Example 2 and Comparative Examples 6 and 7 were observed with a scanning electron microscope JSM-IT300HR manufactured by JEOL Ltd., and the results are shown in FIGS. 1 to 6 , respectively.

All of the silver films obtained in Examples 1 to 12 had a glossiness of 0.0 and an arithmetic mean roughness of 0.30 μm or more. The color tone is white, and it has a good appearance without unevenness. Moreover, as illustrated in FIGS. 1 and 2 , the bulk crystals are uniformly precipitated. Bath stability is also good.

All of the silver films obtained in Comparative Examples 1 to 4 had a glossiness of 0.1 or more, and an arithmetic mean roughness of less than 0.30 μm. The color tone is white, and it has a good appearance without unevenness. Bath stability is also good.

The glossiness of the silver films obtained in Comparative Examples 5 and 6 was 0.0, and the arithmetic mean roughness was less than 0.30 μm. The color tone is white, and it has a good appearance without unevenness. Bath stability is also good. The inventors of the present invention found that even if an iodide salt was used instead of thiosulfuric acid, the silver plating was roughened, but as shown in Figs. Inside, it is hard to say that the appearance is uniform.

The glossiness of the silver film system obtained in Comparative Example 7 was 0.0, and the arithmetic mean roughness was less than 0.30 μm. The color tone is white, and it has a good appearance without unevenness. Moreover, as illustrated in FIGS. 5 and 6 , the size of the crystals is scattered. Bath stability is good.

FIG. 1 is a microscope photograph (370 times) of the silver film obtained in Example 2. FIG. [ Fig. 2 ] A microscope photograph (5000 times) of the silver film obtained in Example 2. [Fig. 3 is a microscope photograph (370 times) of the silver film obtained in Comparative Example 6. FIG. FIG. 4 is a microscope photograph (5000 times) of the silver film obtained in Comparative Example 6. FIG. FIG. 5 is a microscope photograph (370 times) of the silver film obtained in Comparative Example 7. FIG. FIG. 6 is a microscope photograph (5000 times) of the silver film obtained in Comparative Example 7. FIG.

Claims (3)

A kind of electroplating silver liquid is characterized in that containing: Silver cyanide or silver cyanide salt calculated as 10-100g/L in silver conversion, 1～200g/L of conductive salt, with 3～500g/L of thiosulfuric acid or its salt. The silver electroplating solution according to claim 1, wherein the conductive salt is selected from the group consisting of cyanide, phosphate, pyrophosphate, nitrate, citrate, tartrate, thiocyanate, sulfate and boric acid or its salt. At least 1 type of group. As in the silver electroplating solution of claim 1, its pH (25°C) is 7.0 to 13.0.

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