I always thought the copper needed to be super clean, but now I just use Scotch-Brite to give the surface a little tooth and CitraSolv concentrate. CitraSolv is a cleaner, but it is also a solvent for toner (and flux residue). Just go over the copper surface in different directions with the Scotch-Brite and then clean the residue off with CitraSolv (concentrate) until the wipe-off is clear. I usually give the surface a final wipe and let it evaporate. The CitraSolv residue acts as an adhesion promoter for the toner.
Baxter
> Copper needs to be ultra clean. I use 0000 steel wool. followed by scrubbing with TSP solution using scotch brite (green) pad, then rinse with water then cleaned with isopropyl alcohol. Wear glove through out the process. Laminate image immediately to reduce contaminating the copper surface and oxidation. Someone thought oxidizing in the etcher for few second made the image adhere better. Haven't tried so have no comment about oxidizing surface.