Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi all,

I know that I don't post much to this list and act mostly as a lurker, but I
recently tried something that I found on a website (that I am sure many, if
not most on this list have already come across). This will probably end up
a fairly long email, and for that I kind of apologize, but for those that
don't know or never realized, it might be good.

We all know that etching is evil necessity if we wish to make our own
boards - even though many of us utilize mechanical etching via CNC, some
circuit densities don't make that possible unless you have a major high
dollar machine (which of course most of us can't afford).

Well, I, like many others, don't have easy access to etching chemicals -
either we pray that radio shack happens to have a bottle of the nasty stuff,
or we order from a supplier.

I came across a website that mentioned using a muriatic acid and hydrogen
peroxide mix to etch boards. This interested me as it would greatly reduce
the cost of a batch of etchant, and would be much easier to obtain
(considering you can get muriatic acid at local hardware stores.

First a warning: This stuff is major dangerous. if you think ferric
chloride is bad, this stuff makes ferric chloride practically look like
water. Do not attempt to use this stuff if you don't have a very healthy
respect for chemicals and also a well ventilated area.

Second warning: Always always always mix acid to h2o2, never the reverse -
I can't explain why this is important, I am not a chemist, but it has to do
with the way the acid will mix with the water, along with splashing and so
forth.

Second warning: Storage - this stuff is a pain in the arse to store. Once
the seal is broken on the bottle, fumes can escape and start to corode
nearby metal (yes, the fumes from this stuff can easily destroy metal) - I
currently use an outbuilding away from the house to store the excess that I
haven't mixed up. The mixed up batch I neutralized after my experiment and
disposed of. Neutralizing was simply adding an alkaline to it (I used
baking soda, I've read other sites that recommend a watered down amonia
recipe as well - but I'd recommend searching for neutralizing muriatic acid
on the net before attempting)

Well, having used muriatic acid in the past (when I was younger, I used to
be the one to take care of our pool, and it was commonly used as a pool
chemical to change pH levels) I figured this was something I was willing to
try.

The mixture on the site I had read was 50% H2O2 to 50% muriatic acid. THIS
MIX IS TOO STRONG. I mixed at ~33% acid to 67% h2o2 and it was still strong
enough to etch a 4.5x7 board of mostly copper (it was an experiment board
that I had tried on a CNC, so although the board was unuseable, not much
copper was missing) - it etched this thing in <1.5 minutes, I'd say closer
to about 40 or 50 seconds, and this was with very light agitation (mostly
just grabbing the string I had tied around the board and shifting it a
little bit).

It dissolved the copper incredibly fast, and didn't harm anything under the
little etch resist writing I had put on the board.

Final thoughts: Muriatic acid makes a great etchant BUT - it is extremely
dangerous to utilize, and must be utilized in a WELL ventillated area or
outside only. indoor use without sufficient ventilation can be extremely
hazardus. I think a much weaker mix with a longer etch time is desireable,
I'd rather do a 1 to 4 or perhaps a 1 to 5 mix (I may experiment with levels
used to acid wash clean concrete which is 1 to 10) - longer etch with more
safety appeals to me.

I'm also thinking that some of the other concrete cleaning acids may work
well (the ones that are weaker then muriatic acid) with less risk to ones
self.

Also - you need to utilize h2o2, otherwise there will be no good reaction
(something about the extra oxygen molecule that makes the process work) and
it will eat thru the copper, but it will take a very long time.

These are my thoughts and feelings and felt I should share. as I said
before I'm sure many know about this little trick, some probably use it. If
you choose to utilize this method of etching you do so AT YOUR OWN RISK - I
will assume no responsibility if you hurt or kill yourself. I strongly urge
you to search the net on muriatic acid pcb etching to see how others have
done it.

-Tony