Electroplating in presence of co2

Abstract

The present invention provides a method for conducting electroplating in the presence of CO₂ and a metal salt-containing aqueous solution, wherein the CO₂ is in the form of liquid, subcritical or supercritical, the method being characterized in that a nonionic compound having a CO₂-affinitive moiety is further added to the system where the aqueous solution and CO₂ coexist. The method of the present invention improves the efficiency of the electrochemical reaction process and enables formation of an excellent metal film.

Description

TECHNICAL FIELD [0001] The present invention relates to an environmental technology using CO2 as an alternative to conventional solvent. More specifically, the present invention relates to a technique for improving the efficiency of electrochemical reaction by using CO2 as a solvent, and an electroplating technique employing such technique. BACKGROUND OF THE INVENTION [0002] Because of manifestation of various environmental problems, techniques using CO2 as a solvent instead of toxic organic solvents have been attracting public attention. If compounds can be handled in CO2, the cost for treating waste water may be significantly reduced, and therefore the idea of putting a such technique to practical use has been receiving particular attention in dying, plating and like industries which suffer from high waste water treatment costs. Having this as a technical background, a technique wherein CO2 and a metal salt-containing aqueous solution are suspended while stirring, and then electro...

AI Technical Summary

Benefits of technology

[0077] In the present invention, the efficiency of an electroplating reaction can be improved and excellent metal films can be formed by using a nonionic compound having a CO2-affinitive moiety, the nonionic compound having an excellent ability to emulsify CO2 with an aqueous solution of an electrolyte (e.g., metal salt), which is a plating solution, having an excellent ability to remove or defoam bubbles formed during operations, and having a preferable wettability between a substrate, plating solution and CO2. Furthermore, the present invention can simplify the preprocessing and postprocessing conducted before and after plating and significantly improve throughput.

[0078] Use of the nonionic compound of the present invention achieves prompt separation between carbon dioxide and a metal-containing aqueous solution after stirring. This reliably prevents the problems of known techniques, such as bubbles of a metal-containing aqueous solution and carbon dioxide entering pipes and metal salts clogging pipes.

[0079] Furthermore, because the nonionic compound of the present invention exhibits a cleaning ability in supercritical carbon dioxide, it is effective for degreasing conducted prior to plating and washing conducted after plating. Therefore, the present invention greatly contributes to reducing alkaline and acidic waste liquids produced during preprocessing and metal waste liquids produced during washing in postprocessing, which are serious problems in prior art techniques.

Problems solved by technology

However, we reexamined this technique in detail and found that, in order to obtain excellent plated films without pinholes, this technique requires severe restrictions on the conditions for conducting plating, including the selection of a surfactant.

Furthermore, because of its considerable water solubility, a large amount of the polyoxyethylene compound used is also dissolved in a plating solution.

Therefore, separation between the CO2 and the plating solution does not easily progress in the plating bath after plating.

This causes the formation of many bubbles containing the surfactant and plating solution during postprocessing decompression, and the resultant bubbles enter pipes, etc., causing pipes to become clogged.

This problem significantly reduces efficiency in terms of throughput when such techniques are put into practical use.

These surfactants are required to have chemical stability under electrochemical conditions in a plating bath; however, no full examination has been conducted concerning this stability until now.

Furthermore, concerning this supercritical plating technique, no information exists regarding the relationship between the type of surfactant used and the plating ease or resulting plated film.

Images