JPH05331655A - Substitution type electroless gold plating solution - Google Patents

Abstract

(57) [Summary] [Purpose] It is an object to provide a substitution type electroless gold plating solution which suppresses the eutectoid of phosphorus and is excellent in stability. A substitutional electroless gold containing a gold cyanide salt, a phosphite as a reducing agent such as sodium phosphite, and a pH adjusting agent comprising various organic acids or salts thereof and inorganic salts Provide a plating solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substitution type electroless gold plating solution for electrolessly plating a target metal with gold.

[0002]

2. Description of the Related Art In the field of electronics, surface treatment technology is becoming more important and plating is one of them.

Plating is roughly classified into electrolytic plating in which the surface of a cathode object is covered with a metal thin film by utilizing electrodeposition by electrolysis, and electroless plating (chemical plating) in which reduction is caused by the contact action of the material surface. However, since electroplating requires a power source and it is difficult to make the current distribution uniform when it is applied to an article having a complicated shape, electroless plating has been used in recent years.

Among electroless plating, gold plating is used for plating on printed circuits and decoration. As an electroless gold plating solution, for example, potassium gold cyanide is used as a gold salt, and a reducing agent is used as hypoxia. A substitution type electroless gold plating solution comprising sodium phosphate or hydrazine and an organic acid or its salt as a pH adjusting agent and an inorganic salt is known.

This substitution type electroless gold plating solution is frequently used because it forms a stable film when a base metal such as nickel is used as a base (SDSwan and ELGostin; Me).
talFinishing, 59 , 4 (1961)).

[0006]

However, when hypophosphite is used as a reducing agent in the substitutional electroless gold plating solution, H ₂ PO ₂ ⁻ + H ₂ O → H ₂ PO ₃ ⁻ + 2H [Au ( ^{_{CN) 2] - + H →}} Au + HCN + CN - H 2 PO 2 - + H → P + OH - + H 2 O reaction progresses, phosphorus codeposited with gold deposition.

Although many self-catalytic gold plating solutions using borohydrides or borane compounds as reducing agents have been developed, the plating solutions were unstable (Y.Ok
inaka, Plating 57 , 914 (1970) LAD 'Asaro, S.Nakahara
and Y.Okinaka; J.Electrochem.Soc, 127 , 1935 (1980)
).

[0008] Therefore, an object of the present invention is to provide a substitution type electroless gold plating solution which suppresses the eutectoid of phosphorus and is excellent in stability.

[0009]

As a result of intensive studies, the present inventor has found that the use of phosphite as a reducing agent achieves the above object, and has accomplished the present invention.

That is, the present invention provides a substitutional electroless gold plating solution containing a gold cyanide salt, a phosphite as a reducing agent, and a pH adjusting agent.

Examples of the gold cyanide salt include sodium gold cyanide and potassium gold cyanide. However, the gold cyanide salt is not limited to these, and any salt containing a precipitated metal may be used. The concentration of the gold cyanide salt depends on the thickness of the film and the amount of the reducing agent, but it is 1 to 10 g / L.
Is preferred.

Examples of the phosphite include sodium phosphite and potassium phosphite, and the concentration of the phosphite correlates with the concentration of the gold salt, but it is 2-5.
The range of 0 g / L is preferable.

The pH adjusting agent comprises various organic acids or salts thereof and inorganic salts. Examples of the organic acid include citric acid, oxalic acid, acetic acid and the like, and salts thereof include sodium of the above organic acids. Salts, potassium salts and the like can be mentioned, but not limited to these. The concentration of the organic acid or its salt is appropriately added so as to obtain a desired pH, but a range of 10 to 200 g / L is preferable. Further, as the inorganic salt, for example, ammonium chloride can be used, and the concentration thereof is preferably in the range of 20 to 100 g / L. The pH of the plating solution is adjusted to 3 by the pH adjuster.
Adjusted to a range of ~ 8.

The above-mentioned gold cyanide salt, phosphite, and pH adjusting agent are used by dissolving them in water so as to be in the above concentration range, but the dissolving method is not particularly limited, and for example, in a beaker or the like. It may be dissolved while stirring and heating.

After being dissolved in water, it can be used as it is as a plating solution, and plating is performed by immersing the metal to be plated in the plating solution. Here, the material to be plated in the present invention is not particularly limited, but may be a complicated circuit (use for design etc.) in the electronic industry.

[0016]

When a phosphite is used as the reducing agent, the reaction of H ₂ PO ₃ ⁻ + H ₂ O → H ₂ PO ₄ ⁻ + 2H [Au (CN) ₂ ] ⁻ + H → Au + HCN + CN ⁻ proceeds.

Since H ₂ PO ₃ ⁻ + H → P + 3OH ⁻ hardly occurs (H ₂ PO ₂ ⁻ + H → P + O
The number of H ⁻ + H ₂ O is 1/10, and the phosphorus content of the obtained gold plating film can be suppressed low.

[0018]

Example A plating solution having the composition shown in Table 1 was prepared.

[0019]

[Table 1] All units are g / L.

As a result of the experiment, the plating solution (1) of the present invention
In (2), the codeposition of phosphorus in the film is suppressed to 1/10 or less of that in the comparative example.

Further, gold was deposited at 92 to 95 ° C. on the electroless nickel plating film as a base, and the deposition at this time was 4 to 5 μm / hr.

[0022]

EFFECTS OF THE INVENTION The displacement type gold plating solution of the present invention has a stable bath and a high purity of the obtained film. Therefore, it is effective when a film with high gold purity is required.

Claims (1)

[Claims] 1. A substitution type electroless gold plating solution comprising a gold cyanide salt, a phosphite as a reducing agent, and a pH adjuster.