Homebrew PCBs

----- Original Message ----- 
From: "Adam Seychell" <a_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, April 11, 2007 2:02 AM
Subject: [Homebrew_PCBs] printer limitations or etch undercut


>
> derekhawkins wrote:
>>
>>
>>  >I've transferred finer lines with TT that looked ok, but they
>>  >disappeared completely during etching.
>>
>> No surprises there, transferred toner is actually a poor resist in
>> comparison to resist that was developed properly. And when you
>> say "looked ok", what magnification are you referring to?
>>
>> I did that 6/6 rules torture test to debunk a collimation myth. The
>> only reason why it wasn't 5/5 was because the artwork didn't make the
>> grade. I can do less tortuous 5/5 or 4/4 rules (to the limit of the
>> printer) to debunk the etching myth as well. How about .003" or .002"
>> lines with .005" or .004" spacing? What will it take to convince you
>> that etching should be the least of your worries provided you know what
>> you're doing? Do I have to walk on water?
>
> What is your etching technique ?
> What is your foil thickness ?
>
> Ok, you got me curious. Now you've made me waste the past 3 hours of my
> time  determining if etching undercut does indeed limiting line widths.
> My test showed for 18um foil  PCB the limited factor is the printer, and
> not the etch process. I have compile a quick web page showing the
> results of this mornings experiment, enjoy.
>
> http://members.optusnet.com.au/~eseychell/pcbtest1/line_width_tests.html
>
> Even thought my results demonstrated a printer limitation, I still think
> etch undercut can be an issue, especially for bubble etchers or 70um
> ("2oz") foils.

Manual agitation by rocking a container might be best for very narrow lines. 
It's also easier to see what is happening, and it could be combined with 
rubbing the surface with a swab.

Leon