Homebrew PCBs

At 11:53 am ((PST)) Fri Nov 17, 2006, Adi Linden wrote:
>Will aquarium supplies do for building a DIY etching tank? I am thinking
>air pump, heater, air hoese, etc.

Be sure either to follow the pump directions and either install
a non-return valve in the airline or site the pump above the
liquid height.

Otherwise, since the pump delivers warm air, when you switch off
the contraction of the air cooling in the pipe-work may be enough
to start a syphon. Etchant is not likely to benefit your pump... :-(

Also, some types of air-stone may disintegrate in etchant, so you
may need to use a perforated pipe bubble distributor. You need very
small holes and lots of pressure drop across each hole: with large
holes and low pressure, surface tension will tend to bias the airflow
towards only a few of the holes. Using a thick-walled tube will help.

You could make a tank out of glass plates and aquarium silicone
but make sure the joint surfaces are properly cleaned and coated.
Stefan had a leak needing re-work:-  Tue Jul 11, 2006 10:29 am
"Re: Baffled by a bubbler baffle - what are you guys using?".

IIRC it was Stefan who reported elsewhere on 'rapid' epoxy degrading
in the _very_ long term. 24 hour epoxy has generally better chemical
resistance than rapid epoxy, which is especially poor on acid resistance.
There is a lot of stray HCl around with acidic etchants - it's a small
molecule that can penetrate some plastics and then wreak havoc.

>I am torn between building a small vertical etch tank versus
>buying a microwave for heating small quantities of etchant for sponging...

For _small_ quantities, specially buying a microwave seems a bit OTT.

Why not make a double-boiler by sitting a basin in the rim of a pan
of hot water, as for melting chocolate or making delicate sauces?

That shouldn't cost you any more than the price of a dedicated basin
  - nothing, if you can scrounge an old one ;-)

Alternatively (or if you need to transport your warmed etchant to
a cold workshop) you could drop a plastic bottle of etchant into
a bucket of hot water.

PET (fizzy drink bottles) will distort near boiling temperatures but
may prove perfectly usable for this. In a food application (kefir), I find
UK polythene milk bottles are tough enough to withstand microwave
steam sterilization but longer-term begin to crack at the seams
with handling and fermentation pressure. Again, they should prove
quite serviceable (and would be my choice because they are so
plentiful and the opening is larger) - but I wouldn't store etchant
long-term in a thin poly-bottle without a catch tray, just in case.

Of course, bigger plastic jerrican-style bottles are available but you
will need a larger bucket of hot water - unless the cap is large
enough for you to drop in an aquarium heater.

[Please ensure all poisonous liquids are clearly and indelibly labelled,
especially if brightly-coloured or in drinks-like containers, and kept
well out of sight and reach of young children - it's amazing what some
little tykes will consume as a last meal :-(( ... ]


Regards, LenW