For small boards, I wonder if anyone has explored placing the board in a
well-sealed, clear glass or plastic food container, or perhaps something
more elaborate, half-filled with etchant, and then having some vigorous
shaking or rotating arrangement.
I think one of the benefits of the spray approach is that it
preferentially erodes the copper which is directly exposed, without so
much undercutting of the copper under the edge of the photoresist.
I guess shaking, tumbling or ultrasonic agitation would not have this
directional effect.
As I mentioned in a post an hour or so ago, muriatic acid (HCl) may
allow greater visibility of the board, which would help in a clear
container which used shaking, turning over etc. rather than spraying.
However, Edinburgh Etch (ferric chloride and citric acid) is claimed not
to leave any residue, thereby (I guess) reducing the need for agitation
or spraying.
I am currently using a sponge with Edinburgh Etch.
- Robin
http://www.firstpr.com.au/pcb-diy/