The first part of a three step process for multilayer hole preparation. MAGNUM S-400 is used to prepare resinous substrates for subsequent oxidation by permanganate. When used in conjunction with MAGNUM K-OXIDIZER or MAGNUM N-OXIDIZER, it penetrates resin smear for effective desmear and etchback. It is equally effective on epoxy and polyimide resin systems. The solution is replenishable and the boards need not be dried prior to processing.