Reductive electroless gold plating solution, and electroless gold plating method using the plating solution

Abstract

The present invention has an object to provide an electroless gold plating solution capable of suppressing the corrosion of a substrate metal and realizing excellent wire bondability, and containing no hazardous substance. In order to achieve the object, as a reductive electroless gold plating solution used for formation of an electroless plated gold film on a surface of a plating target by electroless plating, an electroless plating solution containing a water-soluble gold compound, citric acid or a citrate salt, ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate salt, hexamethylenetetramine, and a chain polyamine having an alkyl group having 3 or more carbon atoms and 3 or more amino groups is adopted.

Description

TECHNICAL FIELD[0001]The invention disclosed in the present filing relates to an electroless gold plating solution, an electroless gold plating method using the electroless gold plating solution, and a plated product obtained by plating by the electroless gold plating method. More specifically, the invention relates to reductive electroless gold plating technology capable of plating directly a surface of a plating target.BACKGROUND ART[0002]In recent years, while requirements for higher performance and higher multi-function of electronic devices have been raised, further downsizing has been demanded on printed wiring boards used in these electronic devices. In order to cope with the downsizing, micronization of circuit patterns is progressing and along with the micronization of circuit patterns, advanced mounting technologies have been demanded. Generally in the field of printed wiring boards, as technologies of joining mounting components and terminal components, technologies using...

AI Technical Summary

Benefits of technology

The present invention is related to a reductive electroless gold plating solution which contains a water-soluble gold compound, citric acid or a citrate salt, ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate salt, hexamethylenetetramine, and a chain polyamine having an alkyl group having 3 or more carbon atoms and 3 or more amino groups. This solution makes it easy to deposit a thick plated gold film onto a surface of a plating target. The solution also helps to prevent the dissolution of nickel and the diffusion of nickel in the plated gold film, resulting in a high junction reliability of wire bonding. The reductive electroless gold plating solution is stable and safe without any toxic substances. It has excellent selective deposition properties, avoiding the formation of plated gold film on portions where deposition is not needed, saving raw material.

Problems solved by technology

The electroless gold plating method of the Patent Literature 1 has such a problem gold dissolves and corrodes substrate nickel, and nickel thereby diffuses in a plated gold film, however, since the immersion plated gold film is formed by depositing gold by utilizing the difference in redox potential between nickel that is a substrate and gold ions in the plating bath.

When nickel diffuses in the plated gold film, there arises a problem that the gold-gold junction strength in wire bonding decreases.

The technology poses a problem of causing a rise in cost and poor productivity, however, since formation of the immersion plated gold film is essentially needed.

Further in the cases of the electroless gold plating method described in Patent Literature 2 described above and of using a reductive deposition-type electroless gold plating solution for a palladium film described in Patent Literature 3 described above, although the corrosion of nickel that is a substrate metal is enabled to be suppressed, since the electroless gold plating bath contains formaldehyde or a formaldehyde bisulfite salt adduct, which is strongly toxic, it becomes difficult for the safety in plating work to be secured.

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