Abstract: The present invention relates to a method for treatment of recessed structures in a dielectric material for smear removal during the manufacture of printed circuit boards, IC substrates and the like. The dielectric material is contacted with an aqueous solution comprising 60 to 80 wt.-% sulfuric acid and 0.04 to 0.66 mol/l peroxodisulfate ions peroxodisulfate ions and at least one stabilizing additive selected from alcohols, molecular ethers and polymeric ethers. Smear is removed from the recessed structures by the method according to the present invention without penetration of process chemicals into the dielectric material and a sufficiently low copper etching rate is achieved. Furthermore, the shelf life of said aqueous solution is improved even in the presence of copper ions.