NON-CYANIDE ELECTROLESS GOLD PLATING SOLUTION AND PROCESS FOR ELECTROLESS GOLD PLATING

Abstract

The non-cyanide electroless gold plating solution according to the invention is a non-cyanide electroless gold plating solution free from a cyanide compound, wherein bis-(3-sulfopropyl)disulfide is added, as a complexing agent for gold stabilization, to the electroless gold plating solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory drawing illustrating the portion of a substrate to be subjected to electroless gold plating.

FIG. 2 is a graph illustrating hydrogen generation potential of each of a solution to which a conductive salt is added, a solution to which the conductive salt and MES are added, and a solution to which the conductive salt and SPS are added and gold deposition potential of each of a solution of the complex of the conductive salt and an Au-MES complex and a solution of the complex of the conductive salt and an Au-SPS complex.

FIG. 3 is a photograph of the surface of a metal layer made of medium-phosphorus type Ni—P, after forming a gold layer thereon using a non-cyanide electroless gold plating solution according to the invention and then stripping the gold layer.

FIG. 4 is a photograph of the surface of a metal layer made of medium-phosphorus type Ni—P, after forming a gold layer thereon using a non-cyanide electroless gold plating solution according to Comparative Example 2 and then stripping the gold layer.

FIG. 5 is a photograph of the surface of a metal layer made of medium-phosphorus type Ni—P, after forming a gold layer thereon using a cyanide-containing electroless gold plating solution according to Comparative Example 3 and then stripping the gold layer.

FIG. 6 is an explanatory drawing illustrating results of the ball pull test when a tensile force is applied to a solder ball formed on the gold layer formed by electroless gold plating in Example, Comparative Example 2, and Comparative Example 3.

FIG. 7 is an explanatory drawing illustrating a broken mode of a solder ball when a tensile force is applied to the solder ball formed on a gold layer formed by electroless gold plating.

FIG. 8 is a graph illustrating breaking strength (ball pull strength) at which the solder ball is broken when a tensile force is applied to the solder ball formed on a gold layer formed by electroless gold plating.

Claims

1. A non-cyanide electroless gold plating solution free from a cyanide compound, comprising: bis-(3-sulfopropyl)disulfide as a complexing agent for gold stabilization.

2. The non-cyanide electroless gold plating solution according to claim 1, wherein a pH value is 7 or lower.

3. The non-cyanide electroless gold plating solution according to claim 1, further comprising: thallium (Tl) as an accelerator of deposition rate.

4. The non-cyanide electroless gold plating solution according to claim 1, wherein a gold source is a gold sulfite salt or a chloroaurate salt.

5. A process for electroless gold plating, comprising: a step of forming a gold layer, by electroless gold plating, on a metal surface exposed at a bottom surface of a concave portion that is opened in a resinous mask layer covering one surface of a substrate, whereinthe non-cyanide electroless gold plating solution according to any one of claims 1 to 4 is used as a non-cyanide electroless gold plating solution for dipping the substrate.

6. The process for electroless gold plating according to claim 5, wherein an underlying metal layer whose metal surface is exposed at a bottom surface of a concave portion of the substrate is a medium-phosphorus type Ni—P plated metal layer having a phosphorus content in the plated film of 6 to 9% by weight.