The invention concerns processes and solutions for the treatment of copper alloy surfaces, which are subsequently to be firmly bonded to polymeric material. The solution is used, in particular for firmly bonding lead frames to encapsulating molding compounds (polymeric material). The solution contains an oxidant, at least one acid, at least one adhesion-enhancing compound characterized in that the solution additionally contains fluoride ions in an amount of at least 100 mg per litre and chloride ions in an amount of 5 to 40 mg per litre. The solution is particularly useful for treatment of copper alloy surfaces, containing alloying elements selected from the group consisting of Si, Ni, Fe, Zr, P, Sn and Zn.