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Method for On-Line Removal of Gold (Iii) From Gold (I) Plating Solutions

IP.com Disclosure Number: IPCOM000035644D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Bindra, P: AUTHOR [+4]

Abstract

Gold plating is of critical importance to the electronics industry. Gold is corrosion resistant and has a low contact resistance. Use of thin, plated gold films minimizes the expense of device fabrication requiring these properties; however too thin a film will be porous, while too thick a film wastes resources. Control of plated gold film thickness is usually carried out by monitoring the plating time and current density to determine total charge plated per unit area. This method assumes gold exists in the plating solution as the monovalent (Au(I)) species. In reality, trivalent gold ions (Au(III)) are often formed during electroplating by oxidation of Au(I) at the anode of the plating cell.

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Method for On-Line Removal of Gold (Iii) From Gold (I) Plating Solutions

Gold plating is of critical importance to the electronics industry. Gold is corrosion resistant and has a low contact resistance. Use of thin, plated gold films minimizes the expense of device fabrication requiring these properties; however too thin a film will be porous, while too thick a film wastes resources. Control of plated gold film thickness is usually carried out by monitoring the plating time and current density to determine total charge plated per unit area. This method assumes gold exists in the plating solution as the monovalent (Au(I)) species. In reality, trivalent gold ions (Au(III)) are often formed during electroplating by oxidation of Au(I) at the anode of the plating cell. The presence of gold (III) reduces the efficiency of the plating process and reduces the accuracy of plated film thickness control by monitoring plating charge. This is because gold is now being deposited from both the monovalent and trivalent species, and the relationship between current passed and amount of gold deposited (and hence thickness) is not the same for the two species.

A process has been developed which converts Au (III) ions to Au (I) ions in the plating cell during plating, and thus maintains nearly 100% of the gold in the monovalent form.

This process utilizes the fact that the reduction of gold (III) to gold (I). Au(CN)-4 + 2e- T Au(CN)-2 (0.923V SHE) (1) occurs anodic of the reduction of gold (III) to gold metal Au(CN)-4 + 3e- T Au0 + 4CN- (0.678V SHE) (2) and anodi...