Permanganate dirt-removing method for printed-circuit board

Abstract

An improved desmear process for removing resin smeared on an interior wall of a through hole drilled in a resinous substrate, especially resinous substrates made from epoxy, polyimide, cyanate ester resins and bis-maleimide triazine epoxy resins. The process involves contacting the resin smear with a solvent solution to soften the resin smear, followed by treatment with an alkaline permanganate solution to remove the softened resin, and treatment with a neutralizer to neutralize and remove the permanganate residues. The solvent solution comprises a mixture of at least two solvent components, with at least one solvent component being selected from the group consisting of gamma-butyrolactone, ethyl-3-ethoxypropionate, N-ethyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, and N-octyl-2-pyrrolidone. The solvent solution is selective for the softening and removal of epoxy, polyimide, cyanate ester resins and bis-maleimide triazine epoxy resins.

Description

technical field [0001] The present invention relates to a printed wiring board having a through hole, and more particularly to a desmear method and a solvent used in the method for removing resin stains after drilling the through hole. Background technique [0002] A printed wiring board is formed from a layer of conductive material (typically copper or copper or gold plated with solder) on a substrate of insulating material (typically glass fiber reinforced epoxy). Printed circuit boards having two conductive surfaces on opposite sides of one insulating layer are known as "double-sided circuit boards". To accommodate more circuits on one board, several layers of copper are sandwiched between boards or layers of other insulating material to form a multilayer board. [0003] To make an electrical connection between two or more circuit layers on opposite sides of a double-sided circuit board, holes are first drilled through the two conductive circuit layers and the insulating...

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