[sdiy] etching really fine tracks on a pcb

[Heiko van der Linden]

Hi all,

I have a question that's not totally related to synths, but about making the
PCBs..

I am currently trying to make a small pcb for a PSOC with very fine tracks.
I do
the lithography and ethcing myself. The lithography is done with a
commercial
exposure box and looks very sharp. But after etching with ammonium
persulphate I
see that fine tracks near the edge of the board are thin compared to similar
width
tracks near the middle of the board.
I did some tests and found that the way I am etching the boards creates this
problem.
I have a big beaker which I fill with the etchant (around 70 Celsius) and
while holding
the board with a tweezer I move it rapidly from left to right and back. This
causes
vortices at the board edges and a higher etching rate near the board edges.

I was wondering if people have a solution for this problem. I was personally
thinking
about buying a foam etcher or spray etcher, but having no experience with
these machines
I figured asking the gurus here first...

To give an idea of the track widths that I am trying to achieve 100
micrometers is in
the right ball park...

Cheers,
Heiko