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Processing Solution for Base Chrome Etching

IP.com Disclosure Number: IPCOM000037865D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Light, DN: AUTHOR [+3]

Abstract

Chrome-Copper-Chrome layered metallurgy is frequently used for circuitization of flexible substrates such as polyimide. The bottom chrome layer enhances adhesion between the metal and polyimide layers; top chrome enhances the corrosion resistance of the circuitry. Circuitry is defined from blanket metal layers by selective etching of the material to leave circuit lines. The metals are often etched in three steps: both chrome layers can be etched by a potassium permanganate/potassium hydroxide solution, separated by a ferric chloride etch for copper and by several water rinses. Typically the final etching of the base chrome layer is followed by an oxalic acid rinse. Oxalic acid is a weak acid and a weak buffering agent.

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Processing Solution for Base Chrome Etching

Chrome-Copper-Chrome layered metallurgy is frequently used for circuitization of flexible substrates such as polyimide. The bottom chrome layer enhances adhesion between the metal and polyimide layers; top chrome enhances the corrosion resistance of the circuitry. Circuitry is defined from blanket metal layers by selective etching of the material to leave circuit lines. The metals are often etched in three steps: both chrome layers can be etched by a potassium permanganate/potassium hydroxide solution, separated by a ferric chloride etch for copper and by several water rinses. Typically the final etching of the base chrome layer is followed by an oxalic acid rinse. Oxalic acid is a weak acid and a weak buffering agent. It is also a reducing agent and acts to neutralize any residual permanganate on the surface of the substrate. Its acidity also aids in dissolution of any residual copper remaining from the copper etching step, and also helps remove organic residues formed by the interaction of the alkaline permanganate and the polyimide substrate.

Oxalic acid is a weak acid with a pK1 value of 1.23 (pK2 = 4.19). After prolonged use its buffering capacity is diminished and the pH can increase. Under these conditions the oxalic acid cannot effectively remove copper oxide particles that may have formed due to interaction between residual copper on the substrate and the alkaline permanganate solution.

It has been found that a...