Homebrew PCBs

--- Adam Seychell <adam_seychell@...> wrote:

> When it was 
> running a fine aerosol of etchant was forming all
> around the 
> bucket, and you couldn't stand near it or you'll
> choke :)

micro particulant misting... Great for some apps, but
pretty much sucks when corrosive or otherwise
dangerous chemicals are involved. However, I have been
giving this some thought in that I thought it was
going to be an issue.

The micro particulate mist is airborne for two
reasons. It has a strong electrical charge (For a
liquid of it's compostion) and it is close to the
weight of air. The electrical charge is our friend and
is going to help us get rid of the mist and the weight
issue is really a non-issue (As far as impeding the
removal of the mist) because the mist is not lighter
than air. 

The electrical charge was created at moment the
etchant was forced through the plumbing and spray
nozzles at a high pressure/speed. Further,  this is a
common problem in industrial environments that utilize
high pressure and spray nozzles. There are two ways to
fix the problem.  You either reverse the electrical
charge of the micro mist at the nozzle (In this case,
depending on the material(s) that compose the nozzle,
this may not be practical) or you put a plate made of
metal that is corrosive resistant in the etch tank and
give it a strong postive charge (Some apps have a
plate on each wall of the tank). The micro mist will
quickly move to the plate and deposit itself on to
it's surface. It's actually pretty neat to watch...


Best regards


Marvin Dickens
Alpharetta, Georgia  USA

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