Abstract: A 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 or bis-maleimide triazine epoxy resins. The process involves contacting the resin smear with a mixture of gamma-butyrolactone and water to soften the resin smear, followed by treatment with an alkaline permanganate solution to remove the softened resin, and treatment with an aqueous acidic neutralizer to neutralize and remove the permanganate residues. The gamma-butyrolactone is effective as a single solvent for softening and swelling resin smears from substrates made from epoxy, polyimide, cyanate ester resins, bis-maleimide triazine epoxy resins, and polyimide resins.

Abstract: A method for treating a non-conductive through hole surface of a printed wiring board is disclosed. A printed wiring board including through holes is cleaned, conditioned, and a conductive coating is applied to the initially-nonconductive through hole by contacting it with a series of baths. The conductive coating, for example a graphite dispersion coating, facilitates later electroplating of the conductive surface. While at least partially immersing the through hole in one or more of these baths, ultrasonic energy is introduced in the bath in the vicinity of the through hole. The ultrasonic energy can be introduced during the entire immersing step, before the immersing step, or both. The ultrasonic energy reduces the formation of blowholes during later processing (and especially soldering) of the printed wiring board.