Cyanide-based electrolytic roughening silver plating solution

Abstract

According to the present invention, an electrolytic silver plating solution is provided, comprising 10-100 g / L of silver cyanide or silver cyanide salt, 1-200 g / L of conductive salt, and 3-500 g / L of thiosulfate or its salt.

Description

Technical Field

[0001] This invention relates to electrolytic silver plating solutions. Specifically, it relates to electrolytic silver plating solutions formed using silver cyanide as a silver source, and to electrolytic silver plating solutions that yield highly roughened plating films. Background Technology

[0002] Silver, with its white luster, has been used in jewelry since ancient times. Because silver is relatively abundant and inexpensive among precious metals, it is also used in modern decorative applications such as silver ornaments and tableware. Furthermore, silver has the highest electrical conductivity of all metals at room temperature, so silver plating is also widely used for lead frames and substrates in electronic devices such as ICs and transistors. Moreover, because silver has the highest visible light reflectance of all metals, silver plating is frequently used for lead frames and various substrates in light-emitting devices such as LEDs. In addition, silver plating is also used in bearing components and in applications utilizing silver's antibacterial properties.

[0003] To date, various efforts have been made in the semiconductor industry to improve the reliability of IC packages. In particular, roughening plating has been developed to prevent IC package damage known as the "popcorn effect." By roughening the surface of copper or nickel plating, which forms the substrate, the adhesion between the plating and the resin, based on the anchoring effect, is improved. For example, Patent Document 1 describes a technique using two layers of roughening plating to improve adhesion. However, with these conventional techniques alone, the noble metal plating applied to the outermost surface cannot fully realize its anchoring effect. Therefore, a method is desired to roughen silver plating itself, which has excellent electrical properties, and apply it to the outermost surface. On the other hand, silver plating is prone to recrystallization due to heat. Therefore, in the case of silver plating, the anchoring effect may be reduced due to heat treatment, as seen in the needle-like plating observed in typical roughened copper and nickel plating.

[0004] Silver plating solutions using sulfide compounds have been known for a long time. Patent Document 2 discloses a silver plating solution containing thiols and disulfide compounds as a stabilizer for silver converted to cyanide. Patent Document 3 discloses a method for stabilizing the plating solution using thiosulfate. Thus, sulfur compounds, particularly thiosulfate, are utilized as stabilizers and reducing agents, especially in cyanide-free or electroless silver plating solutions. However, because thiosulfate is known as an antidote for cyanide compounds, there are no examples of using thiosulfate or its salts in cyanide-based electrolytic silver plating solutions for the purpose of roughening the plating.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. WO2017 / 077903

[0008] Patent Document 2: Japanese Patent No. 6608597

[0009] Patent Document 3: Japanese Patent No. 3300519 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] Given the above, conventional techniques have not been able to improve the adhesion between precious metals, particularly silver, which has excellent electrical properties and solder wettability, and resin. Furthermore, there are concerns about performance degradation due to recrystallization and the natural growth of whiskers from single-crystal metals on the metal surface, especially concerning needle-shaped silver. Therefore, it is desirable to develop a silver plating solution that produces a roughened silver film in a non-needle-like form.

[0012] The purpose of this invention is to provide an electrolytic silver plating solution for obtaining a highly roughened silver film.

[0013] Methods for solving problems

[0014] The inventors conducted in-depth research and discovered that by adding thiosulfate and / or its salts to the electrolytic silver plating solution, a non-needle-like, highly roughened silver film can be obtained, thus completing this invention. The invention that solves the above-mentioned problems is described below.

[0015] [1] An electrolytic silver plating solution, characterized in that it contains:

[0016] In silver equivalent terms, it is 10–100 g / L of silver cyanide or silver cyanide salt;

[0017] Conductive salts of 1–200 g / L; and

[0018] Thiosulfuric acid and / or its salts at concentrations of 3–500 g / L.

[0019] [2] According to the electrolytic silver plating solution of [1], wherein the conductive salt is selected from at least one of cyanide, phosphate, pyrophosphate, nitrate, citrate, tartrate, thiocyanate, sulfate, and boric acid or its salt.

[0020] [3] The electrolytic silver plating solution as described in [1], wherein the pH (25°C) is 7.0 to 13.0.

[0021] Invention Effects

[0022] The electrolytic roughening silver plating solution of the present invention can stably obtain a non-needle-like, highly roughened silver film. Specifically, as... Figure 1 , 2As shown, a film with a bulk crystal elongation shape can be obtained. Therefore, the possibility of shape deterioration due to recrystallization is small. Furthermore, the large unevenness generated in the direction of plating growth results in a high anchoring effect when bonding with resins, etc. Consequently, stable performance can be obtained, thus improving the manufacturing yield. Attached Figure Description

[0023] Figure 1 Microscopic image (370x) of the silver coating obtained in Example 2.

[0024] Figure 2 This is a microscope image (5000x) of the silver coating obtained in Example 2.

[0025] Figure 3 Microscopic image (370x) of the silver coating obtained in Comparative Example 6.

[0026] Figure 4 Microscopic photograph (5000x) of the silver coating obtained in Comparative Example 6.

[0027] Figure 5 Microscopic image (370x) of the silver coating obtained in Comparative Example 7.

[0028] Figure 6 Microscopic image (5000x) of the silver coating obtained in Comparative Example 7. Detailed Implementation

[0029] The electrolytic silver plating solution of the present invention contains a silver cyanide complex at a concentration of 10 to 100 g / L (based on silver content) as a silver salt, a conductive salt at a concentration of 1 to 200 g / L, and thiosulfate or a salt thereof at a concentration of 3 to 500 g / L. The components constituting the electrolytic silver plating solution of the present invention will be described below.

[0030] [Silver cyanide complex]

[0031] In the electrolytic silver plating solution of the present invention, known silver cyanide complexes can be used as the silver source without limitation. Examples of silver cyanide complexes include silver cyanide, potassium silver cyanide, and sodium silver cyanide.

[0032] Regarding the concentration of the silver cyanide complex in the electrolytic silver plating solution of the present invention, the silver ion concentration is preferably 10 to 100 g / L, more preferably 20 to 70 g / L. When the silver ion concentration is less than 10 g / L, the deposition efficiency decreases, and sometimes the desired silver film thickness cannot be obtained. On the other hand, when the silver ion concentration exceeds 100 g / L, the loss of silver salts due to carryover from the plating solution by the plated object increases, which is uneconomical.

[0033] [Conductive Salt]

[0034] The conductive salts incorporated into the electrolytic silver plating solution of the present invention are not particularly limited as long as their aqueous solutions are conductive. For stable industrial use and economical production of the electrolytic silver plating solution, it is preferable to contain at least one salt selected from cyanide, phosphate, nitrate, citrate, tartrate, thiocyanate, sulfate, and boric acid or its salts. Furthermore, soluble organic acid salts are also preferred. These can be used alone or in combination of two or more. Examples of cyanides include potassium cyanide and sodium cyanide. Examples of phosphates include potassium phosphate, sodium phosphate, and ammonium phosphate. Examples of pyrophosphates include potassium pyrophosphate, sodium pyrophosphate, and ammonium pyrophosphate. Examples of nitrates include potassium nitrate, sodium nitrate, and ammonium nitrate. Examples of citrates include potassium citrate, sodium citrate, and ammonium citrate. Examples of tartaric acid include potassium tartrate, sodium tartrate, and potassium sodium tartrate. Examples of thiocyanates include potassium thiocyanate and sodium thiocyanate. Examples of sulfates include potassium sulfate, sodium sulfate, and ammonium sulfate. Examples of boric acid or its salts include boric acid, sodium borate, and potassium borate.

[0035] The concentration of the conductive salt in the electrolytic silver plating solution of the present invention is preferably 1 to 200 g / L, more preferably 10 to 200 g / L, and particularly preferably 20 to 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, making it impossible to perform plating with an appropriate cathode current density.

[0036] [Thiosulfate (salt)]

[0037] The thiosulfate and / or its salts (hereinafter referred to as "thiosulfate (salt)") used in the electrolytic silver plating solution of the present invention can specifically include thiosulfate, potassium thiosulfate, sodium thiosulfate, etc. They can be used alone or in combination of two or more.

[0038] The concentration of thiosulfate (salt) in the electrolytic silver plating solution of the present invention is preferably 3-500 g / L, more preferably 3-300 g / L, and even more preferably 3-150 g / L. When the concentration of thiosulfate (salt) is less than 3 g / L, the shape and size of the precipitated silver crystals are not uniform. When the concentration of thiosulfate (salt) exceeds 500 g / L, precipitation may occur.

[0039] [Other ingredients]

[0040] In the electrolytic silver plating solution of the present invention, in addition to the above-mentioned components, surfactants and other components may be included to reduce viscosity and suppress unevenness of the silver film, without compromising the purpose of the present invention. Examples of surfactants include anionic surfactants such as sodium polyoxyethylene alkyl ether sulfate and nonionic surfactants such as polyoxyethylene alkyl ether condensates.

[0041] The electrolytic silver plating solution of the present invention can be manufactured by dissolving the aforementioned silver cyanide or silver cyanide salt, conductive salt, thiosulfate and / or its salts, and other components as needed in water. Alternatively, it is preferable to pre-dissolve the conductive salt, thiosulfate and / or its salts, and other components as needed in water, and then add silver cyanide or silver cyanide salt during use.

[0042] The electrolytic silver plating solution of the present invention is preferably used at a pH of 7.0 to 13.0 (25°C, the same below), and more preferably at a pH of 8.0 to 13.0. When the pH is less than 7.0, the cathode current efficiency decreases, and the resulting film does not achieve sufficient thickness. When the pH exceeds 13.0, the appearance of the resulting film deteriorates.

[0043] The preferred temperature of the electrolytic silver plating solution of the present invention is 10–80°C, more preferably 20–60°C. When the temperature of the plating bath deviates from the above range, the cathode current efficiency may decrease or the stability of the plating bath may be compromised.

[0044] The current density when using the electrolytic silver plating solution of the present invention can be set taking into account the composition of the plating solution, the liquid temperature, and other conditions. For example, when using the plating solution at a liquid temperature of 60°C, the current density is preferably set to 30–100 A / dm. 2 When the current density is not set appropriately, abnormalities may occur in the appearance and characteristics of the plating film. Additionally, the plating bath may become unstable, leading to the decomposition of the plating solution components.

[0045] Example

[0046] The present invention will now be specifically described through examples. However, the present invention is not limited to these examples.

[0047] (Examples 1-12, Comparative Examples 1-7)

[0048] As the object to be plated, use 0.1dm 2 The copper plate was first degreased with an alkaline degreasing solution, then neutralized with dilute sulfuric acid. Following this, a matte copper plating of approximately 1.7 μm was performed using a cyanide bath. Then, a silver plating of approximately 0.1 μm was performed using a cyanide-based strike bath.

[0049] The plating solutions for Examples 1-12 and Comparative Examples 1-7 were prepared using the compositions described in Tables 1 and 2. 0.5 L of the prepared plating solution was pumped up and brought into contact with the substrate, which was shielded by a 1 cm square area. Electrolytic silver plating was performed under the conditions described in Tables 1 and 2 until the silver film thickness reached 4 μm. After washing with clean pure water, the substrate was dried.

[0050] For the silver films of Examples 1-12 and Comparative Examples 1-7 obtained above, gloss and arithmetic mean roughness were measured. The gloss referred to here is the value measured by a densitometer ND-11 manufactured by Nippon Denshoku Kogyo Co., Ltd. The arithmetic mean roughness referred to here is the value obtained by resolving the roughness using a shape measurement laser microscope VK-9700 manufactured by Keyence Co., Ltd. at 150x magnification. The measurement results are shown in Tables 1 and 2.

[0051] Furthermore, regarding the silver films of Examples 2, 6, and 7, the results observed using a scanning electron microscope JSM-IT300HR manufactured by Nippon Electron Ltd. are shown below. Figures 1-6 .

[0052] [Table 1]

[0053]

[0054] [Table 2]

[0055]

[0056] Regarding the silver films obtained in Examples 1-12, the gloss level was 0.0, and the arithmetic mean roughness was 0.30 μm or higher. The color was white, without unevenness, and had a good appearance. Furthermore, as... Figure 1 , 2 As illustrated, it precipitates uniformly in bulk form. The bath stability is also good.

[0057] Regarding the silver films obtained in Comparative Examples 1-4, the gloss was all above 0.1, and the arithmetic mean roughness was all less than 0.30 μm. The color was white, without any unevenness, and had a good appearance. Bath stability was also good.

[0058] For the silver films obtained in Comparative Examples 5 and 6, the gloss was 0.0, and the arithmetic mean roughness was less than 0.30 μm. The color was white, without any unevenness, and had a good appearance. Bath stability was also good.

[0059] The inventors discovered that even when using iodide salts instead of thiosulfate (salt), silver plating can be roughened, but... Figure 3 , 4 As illustrated, the needle-like and plate-like silver crystals precipitate, and their appearance is difficult to describe as uniform when confirmed by an electron microscope.

[0060] Regarding the silver film obtained in Comparative Example 7, the gloss is 0.0, and the arithmetic mean roughness is less than 0.30 μm. The hue is white, without unevenness, and has a good appearance. Furthermore, as... Figure 5 , 6As illustrated, the crystals are of scattered size. The bath exhibits good stability.

Claims

1. An electrolytic roughening silver plating solution, characterized in that, contain: In silver equivalent terms, it is equivalent to 10~100g / L of silver cyanide or silver cyanide salt; Conductive salts of 1~200 g / L; and 20~500g / L of thiosulfate or its salt.

2. The electrolytic roughening silver plating solution according to claim 1, wherein, The conductive salt is selected from at least one of cyanide, phosphate, pyrophosphate, nitrate, citrate, tartrate, thiocyanate, sulfate, and boric acid or its salts.

3. The electrolytic roughening silver plating solution according to claim 1, wherein, The pH is 7.0~13.0 at 25℃.

Images