Browse Prior Art Database

Oxalate-Containing Soft Gold-Plating Bath

IP.com Disclosure Number: IPCOM000039871D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Bindra, P: AUTHOR [+4]

Abstract

A novel supporting electrolyte for gold-plating baths leads to soft, fine-grained films suitable for wire-bonding substrates. The bath is comprised of inter alia, an organic oxalate, anion, which prevents the buildup of gold (III) ions in the bath during plating and permits a uniform plating efficiency over time. More specifically, the supporting electrolyte contains mono and di-hydrogen potassium phosphate as a buffering system, thallium as a grain refiner and softening agent, and an anionic agent, potassium oxalate. Potassium gold cyanide is used as a source of gold (I) ions. The unique composition of the bath of this invention enables it to maintain the gold (III) concentration at a constant, near-zero level.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 99% of the total text.

Page 1 of 1

Oxalate-Containing Soft Gold-Plating Bath

A novel supporting electrolyte for gold-plating baths leads to soft, fine-grained films suitable for wire-bonding substrates. The bath is comprised of inter alia, an organic oxalate, anion, which prevents the buildup of gold (III) ions in the bath during plating and permits a uniform plating efficiency over time. More specifically, the supporting electrolyte contains mono and di-hydrogen potassium phosphate as a buffering system, thallium as a grain refiner and softening agent, and an anionic agent, potassium oxalate. Potassium gold cyanide is used as a source of gold (I) ions. The unique composition of the bath of this invention enables it to maintain the gold (III) concentration at a constant, near-zero level. The reduction of gold (III) ions to gold (I) is described in the following equation: Au(CN)-4 + 2-e + 2H+ T Au(CN)-2 + 2HCN Because the potential at which this reaction occurs is anodic of the potential for oxalate oxidation, the presence of an excess of oxalate anions in the bath tends to prevent formation of gold (III) at the anode, and reduces any gold (III) formed back to gold (I). By preventing the buildup of gold (III) in the bath, oxalate allows a constant plating efficiency, and thus the accurate determination of film thickness based on plating time and current density. A further advantage of the presence of oxalate anions in the bath is that they enhance the buffering capacity and stability of the phospha...