For my Homebrew Projects, I have had varying degrees of success at cleaning PCB Material for use with the Toner Transfer process.
The most success seems to come from scrubbing the PCB Material with Scotch-Brite while under running water with soap. I try to clean the copper until the water beads-up and runs off. Sometimes this happens, and other times it does not seem to work as well. If it does not look right, I follow-up with Alcohol, Acetone or Brake-Cleaner.
Inadvertently, I discovered my success was dependent on the type of soap I used, Simple Green seems to sheet the water off, and Boraxo Hand Soap beads the water off. Obviously one of the two methods is leaving (or removing) something that is potentially, beneficial, or harmful, to the following Toner Transfer process.
The Boraxo cleaning method makes the board "look-the-best" and requires little or no drying - but I wonder if it is really clean, or is it a False-clean?
The Simple Green cleaning method requires drying, and so far I have used paper towels to "pat" the surface to dry. But, I think the paper towels may have chemicals that may be detrimental to the Toner Transfer process. Note: My Dad worked in a paper factory, and once said, "paper towels have rosin in them and that is what makes you nose red or raw if you use them as a tissue".
Should water bead-up or sheet-off of clean copper? I am not sure if I know how to find the real answer. It could make a big difference in the success or failure of my repeatable Thin Trace (5mils or less) Toner Transfer process.
Google does not help, most articels provide information on how to clean pennies or cookware, and then they suggest the addition of a protective ware-layer. Nothing I have found provides information on how to clean to real bare copper.
My new Shop location uses well water (the previous shop was on a city water supply, of processed lake water), I wonder if the well water is more or less deterministic for my success? I may try some distilled water, but I do want to kept it simple,
I need to investigate how to "cleaning copper" further.