Homebrew PCBs

so it seems...

h2o2 is a wonderful oxydizer...
just make sure not to generate lots of clorine gas when using with 
hcl/fe3cl.
you will smell this.
then it is too much concentrated (and who realy needs a board in 10 
seconds).
be very careful to avoid "boiling". this can get very dangerous because the 
heating can start a chain reacion.
use only in small amounts. there were people killed in industrial shops 
when the solution went "crazy" in the past.
also be aware that the bursting bubbles spit small amounts of etchant 
around. use high walled container or cover.

but if the above is regarded it is really a nice thing... also it is a lot 
cheaper than i expected.
wear proper protection and always keep water at reach... (to cool solution 
if it gets too crazy and to wash your hands instantly, use
it to flush boards too).

and notice of the heat generated while etching. this gives you a clue how 
high you are up with your concentration level.

i found out that it is only so much h2o2 needed to keep the etchant light 
bright green.
then there is not so much bubbling (which causes under-etching because all 
is damn fast).
when it is used up it turns dark green, little like brown. simply add h2o2 
and it gets green again.
sometimes a hard to etch spot is left in the middle of the pcb.
if you gradually add new h2o2 when it gets brown you actually put it in 
exactly over the middle where the copper is thick.
so you can adjust where it etches most. dont move it for some seconds.
with some experience you can easily get a pcb etched very even, not 
exposing the border tracks to underetching because
the center is slower etched.
but this works only in flat tray etching and may not be needed at all if 
the tracks are not too thin.
i also discovered the arangement of tracks changes ethching rate (on spots 
with only few tracks it takes longer, the neighbouring areas get 
"accelerated" by the unused etchant over the traces.)

i think that's all i know about it...
next pcb will be made soon... a speed controller for rc plane.
but my drill stand i still didn't construct (but having most of the pieces) 
.

stefan


On Wed, 2 Jul 2003 17:14:31 +0100, Leon Heller <leon_heller@...> 
wrote:

> My ferric chloride etchant was obviously exhausted, when I was etching a
> couple of small boards this afternoon, so I sloshed in some H2O2, 
> reasoning
> that it would oxidise any cuprous chloride to cupric chloride - an 
> etchant
> in its own right, and convert ferrous chloride back to ferric chloride.
> There was a lot of fizzing and the board finished etching in seconds. I 
> had
> previously added some HCl to prevent sludge build-up.
>
> Leon
> --
> Leon Heller, G1HSM
> leon_heller@...
> http://www.geocities.com/leon_heller
>
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