On Sat, 26 Nov 2011 20:07:42 -0800, mkoblic wrote:

I was testing a new batch of CuSO4 solution for electrolytic etching on
a scrap piece of brass. The result is he

http://www.flickr.com/photos/2768312...in/photostream

I am puzzled at the circular defects which are exclusively associated
with the numbers. The only answer I could think of was more bubbles, but
why? This is a process that does not generate any gas so unless it is
the dissolved air coming out due to heating (about 25W dissipated in the
bath) I just cannot explain it. Also, why are the defects present only
inside or over the numbers? I do not see them anywhere else.

I have done electrolytic etching with brass before but not a "positive"
etch like this one. Never seen a similar phenomenon before.

On the bright side the steel etching is working like magic:

http://www.flickr.com/photos/2768312...in/photostream

The brass stuff does look an awful lot like bubbles clinging to your
resist. How opaque is your CuSO4? Can you visually monitor the process?

If you are using something like vinyl letters for resist, and there is
air trapped under the letters then it might expand and come out with heat
-- but if that were the case I would expect some undercutting.

When folks etch circuit boards they gently agitate the etchant, the
board, or both -- the two methods that I've experienced personally are to
keep tilting the tray with the board and etchant, or to put the board
edge-on into a bath that has a bubbler on the bottom.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com