Before it can be used, the blank circuit board must be clean. Immaculately clean. No dust, or fingerprints, or specks of oil, and no oxide layer. It is best to do this immediately before making the circuit board so the copper does not have time to oxidize. Oxidized copper traps oil, prevents the resist from sticking, prevents the PCB etchant from etching, and can't be soldered.
Steps Involved
There is an order that should be followed when cleaning a circuit board:
1.Remove the oxide layer (the tarnished-looking surface).
2.Remove the oil (degrease).
3.Protect the surface from exposure to more grease and oxygen.
Removing the Oxide Layer from the Circuit Board
Removing the oxide layer is important as a first step, because the oxide layer is porous, and traps oil and grease. To remove the oxide layer from the circuit board you can use a Scotchbrite™ pad, or fine sandpaper. You scrub the surface under running water until it is bright metalic looking. The whole surface must be this way. Another way is to use a moulding sanding block. It is semi-soft block of abrasive material that ablates off to take the shape of the surface being sanded. This odd material is the same thing some printed circuit board shops use to remove the oxide layer and deburr the drilled circuit boards. Of course they use a machine, typically looking like a big surface sander or planer. They feed the drilled panel in one side and it comes out the other side with no oxide layer or burrs.
Degreasing the Circuit Board
The degreaser I use is Dawn dishwashing soap. It works, and is available everywhere. Apply a little to a Scotchbrite pad and scrub from one end to the other, then do it again. Rinse it thoroughly in tap water. Then rinse in distilled water or filtered water. I have an RO filter and a little tap on the kitchen sink that works fine.
There are those who suggest using solvents after this point, but I disagree. The solvents, with the exception of pure alcohol, all leave residue on the circuit board when they evaporate. The final step in that case is to rinse the residue off with alcohol. If you don't put the solvents on in the first place, you don't need to rinse them off. Anyway, that's my theory and it seems to work.
You can tell when the circuit board is clean by rinsing it thoroughly and then running water on it slowly, while holding it horizontal. The water should sheet - not bead. You have to rinse well, because this is the same sign the circuit board shows when the degreaser is not completely rinsed off. If you need to, use a cotton ball as a swab to help rinse the off the degreaser.
Protecting the Circuit Board Surface
If you are not going to use the circuit board immediately, you should put it in a folded piece of paper and put something flat on it. You could put it in a book, for instance. That will keep the air from getting to it and forming another oxide layer. Most importantly, don't touch the surface with your fingers, or anything that has oil on it.
