JP2014019885A - Non-cyanogen electroless gold plating bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable non-cyanogen electroless gold plating bath.SOLUTION: A non-cyanogen electroless gold plating bath 1 includes: gold ions; 2-aminoethanethiol that is a main complexing agent; at least any of citrate ions or tartaric acid ions that are auxiliary complexing agents; and a reductant of the gold ions.

Description

  The present invention relates to a non-cyanide electroless gold plating bath containing a complexing agent that stably holds gold ions.

  The gold plating film has excellent electrical characteristics, corrosion resistance, solderability, and the like. For this reason, it is frequently used in the manufacture of electronic components including wiring boards. It is also widely used for decoration because of its unique luster and color.

  As a gold plating bath, a cyan bath to which a cyanide compound is added has been used for many years in order to stably hold gold ions in the bath. However, the cyan bath not only requires careful handling and storage due to its toxicity, but also damages the resist, so it cannot be used for plating a wiring board having a fine resist pattern.

  For this reason, various non-cyanide plating baths have been proposed. For example, Japanese Patent Application Laid-Open No. 2006-111960 discloses a non-cyanide substituted plating bath having thiouracil, aminoethanethiol, methylthiourea, aminomercapto-triazole, dihydroxymercaptopyrimidine, or mercaptonicotinic acid in order to keep gold ions stable. Is disclosed. Further, the publication discloses a non-cyanide substitution plating bath containing aminoethanethiol and citrate ions.

  JP 2000-26977 A discloses mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, glucosecysteine, 1-thioglycerol, sodium mercaptopropanesulfonate, N-acetylmethionine. Noble metal electroless plating bath using thiosalicylic acid, 2-thiazoline-2-thiol, 2,5-dimercapto-1,3,4-thiadiazole, 2-benzothiazole thiol, or 2-benzimidazole thiol as a reducing agent Has been.

  However, a more stable non-cyanide electroless gold plating bath has been demanded.

JP 2006-111960 A JP 2000-26977 A

  An embodiment of the present invention aims to provide a stable nocyanide electroless gold plating bath.

  The non-cyanide electroless gold plating bath of the embodiment of the present invention includes gold ions, 2-aminoethanethiol as a main complexing agent, and at least one of citrate ions or tartrate ions as auxiliary complexing agents, and the gold An ionic reducing agent.

  According to the embodiment of the present invention, a stable non-cyanide electroless gold plating bath can be provided.

It is a schematic diagram for demonstrating film-forming of the gold plating film by the no cyanide electroless gold plating bath of embodiment.

  As shown below, the plating bath 1 of the embodiment (see FIG. 1) includes at least gold ions, 2-aminoethanethiol as a main complexing agent, and citrate ions or tartrate ions as auxiliary complexing agents. A non-cyanide electroless gold plating bath containing any one and a reducing agent for gold ions. Hereinafter, “mol / liter” is abbreviated as “M”.

<Plating bath 1>
Sodium chloroaurate 0.005M
2-Aminoethanethiol 0.025M
Citric acid 0.125M
Bipyridyl 100ppm
PEG200 100ppm
Sodium hypophosphite 0.02g / L (G)
Bath temperature: 80 ° C
pH 5 (adjusted with potassium hydroxide)

  As a source of gold ions, a gold salt such as chloroaurate or gold sulfite can be suitably used. From the viewpoint of cost, handleability, and formation of a stable complex described later, a gold salt having trivalent gold is used. Certain sodium chloroaurates are particularly preferred.

  The concentration C of gold ions is preferably 0.001 to 0.1M. If the concentration is above the above range, the precipitation reaction proceeds stably, and if it is below the above range, it is economical and precipitation does not occur. .

  The concentration M of 2-aminoethanethiol as the main complexing agent is preferably 1 to 10 in the ratio (M / C) to the gold ion concentration C, and if it is within the above range, a very stable complex is formed. . For example, when the sodium chloroaurate concentration C is 0.01M, the 2-aminoethanethiol concentration M is set to 0.05M, so that M / C = 5, which is the same as the plating bath 1.

  Various citrates such as citric acid or trisodium citrate anhydrate can be used as a source of citrate ions as an auxiliary complexing agent. Citrate ion is an auxiliary complexing agent and forms a particularly stable complex when used with 2-aminoethanethiol. The citrate ion concentration N, which is an auxiliary complexing agent, is preferably 1 to 50 in terms of the ratio (N / M) to the 2-aminoethanethiol concentration M, which is the main complexing agent. Forms a stable complex. That is, the gold ion concentration C: the main complexing agent concentration M: the auxiliary complexing agent concentration N is more preferably 1: (1-10) :( 1-50). For example, in the plating bath 1, 1: 5: 25. Further, tartrate ions and citrate ions may be used as auxiliary complexing agents. When the auxiliary complexing agent is a salt, the potassium salt is preferable to the sodium salt because the gold plating film has a higher gloss. The names of the main complexing agent and the auxiliary complexing agent are convenient.

  The reason why the complex complex of 2-aminoethanethiol and citric acid exhibits excellent properties for stabilizing gold ions has not been fully elucidated. However, when 2-aminoethanethiol is added after sodium chloroaurate during preparation of the plating bath 1, the yellow solution turns colorless. From this, the trivalent gold ion of sodium chloroaurate is reduced by 2-aminoethanethiol to form a monovalent gold ion when forming a complex, forming a complex complex with citrate ion, which is very stable It is thought to do.

  That is, 2-aminoethanethiol has a reducing power, but when citrate ions coexist, monovalent gold ions form a very stable complex. It is thought that it cannot be reduced.

  Tartrate ions also form stable complex complexes with 2-aminoethanethiol. For this reason, tartrate ions may be used as auxiliary complexing agents instead of citrate ions. However, citrate ions are particularly preferred from the viewpoints of stability and solubility.

  Hypophosphite ion is a reducing agent having a stronger reducing power than 2-aminoethanethiol, and reduces monovalent gold ions forming a stabilized complex to metal. As a source of hypophosphite ions, sodium hypophosphite or potassium hypophosphite is used. As for hypophosphite ion concentration G (g / L), the ratio (G / C) to gold ion concentration C is preferably 1 to 10, and if it is above the above range, the precipitation reaction proceeds stably. If it is below, the plating bath will not self-decompose. For example, when the gold ion concentration is 0.05 M, G / C = 4, which is the same as the plating bath 1, by setting the hypophosphite ion concentration to 0.04 G. As the reducing agent, ascorbic acid, thiourea, DMAB, formalin, hydrazine or the like may be used.

  Bipyridyl and PEG200 (polyethylene glycol having a molecular weight of 200) are so-called brighteners and surfactants, and appropriate amounts are added respectively. As the brightener and surfactant, phenanthroline, picoline (methylpyridine), or the like may be used.

  Potassium hydroxide is a pH adjuster, and sodium hydroxide, potassium hydroxide, aqueous ammonia, sulfuric acid, or the like may be used. The plating bath 1 is a neutral bath having a pH in the range of 6 to 8. However, depending on the type of the reducing agent, the plating bath 1 may be an acidic bath having a pH of 4 to 6 or an alkaline bath having a pH of 7 to 14. Good.

  That is, the gold plating bath of the combination of the main complexing agent and the auxiliary complexing agent in the embodiment exhibits stable characteristics in a wide pH range from acidic to alkaline. As already explained, it is considered that the combination of the main complexing agent having the function of reducing trivalent gold ions to monovalent and the auxiliary complexing agent forms a specifically stable complex. In this stable complex state, the reducing power of the main complexing agent does not reduce the monovalent gold ion to metallic gold, and the monovalent gold ion is reduced to metallic gold only by a reducing agent having a stronger reducing power. The

<Film formation method>
As shown in FIG. 1, COP (cyclofin polymer) is used as the substrate 2, and after a known pretreatment (ultraviolet irradiation treatment, alkali treatment, conditioning treatment, palladium ion treatment, reduction treatment, etc.), 30 minutes in the plating bath 1 Immersion was performed to obtain a shiny gold plating film 3.

  The electroless plating bath 1 was stable even when held at 80 ° C. for 72 hours, and no problem occurred even when stored for 1 month at room temperature.

  That is, the electroless plating bath 1 was very stable.

  On the other hand, the plating bath to which either 2-aminoethanethiol or citric acid was not added was not as stable as the electroless plating bath 1. For example, a plating bath to which no citric acid was added self-decomposed at 80 ° C. for 24 hours.

  The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.

Claims (4)

With gold ions,
2-aminoethanethiol as the main complexing agent;
At least one of citrate ion or tartrate ion as an auxiliary complexing agent,
A non-cyanide electroless gold plating bath comprising a reducing agent for the gold ions.   The non-cyanide electroless gold plating bath according to claim 1, wherein the reducing agent is hypophosphite ion. The gold ion concentration C is 0.001 to 0.1 (mol / liter),
The gold ion concentration C (mol / liter): the main complexing agent concentration M (mol / liter): the auxiliary complexing agent concentration N = 1: (1-10): (1-50). ,
The non-cyanide electroless gold according to claim 1, wherein the gold ion concentration C (mol / liter): the hypophosphite ion concentration G (g / liter) = 1: (1 to 10). Plating bath. The gold ion source is a gold salt with trivalent gold,
The non-cyanide electroless gold plating bath according to claim 2, wherein the trivalent gold is reduced by the action of 2-aminoethanethiol, and the gold ion in the bath is monovalent.

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