Homebrew PCBs

Hi Adam - (and interested list members).

All (I hope)of my equipment and most of my chemicals are now on hand.
The specific gravity of my etchant is 1.245.

I did a trial titration. First I tried titrating until I reached
"turbidity" (whatever that is, I didn't see anything which I thought
might be it.) So I started over.

I put 1 ml of etchant in 20 mL distilled water, and added 4 drops of
Methyl orange. I then dripped 0.1 N NaOH solution into the beaker
until the color changed from orange to yellow. About 17.5 mL of
titrant were used to get to the end point. 

Assuming .31% HCl corresponds to 1 mL of titrant, the acid
concentration is about 5.4%, which is a bit high I guess, but some
etching will bring it down.

I had fun playing mad chemist. When a couple more chemicals arrive I
will try to determine the copper content and see how (if?) it matches
up with the specific gravity. (Luckily I found a photographer with a
100 pound bag of sodium thiosulfate who was happy to send me 100 grams
for the price of stamps. While it is a consituent of some current
photographic "fixers" (to fix the silver structure of the photgraph so
it doesn't change), there are lots of other chemicals included in all
the fixers I found, so I had to go looking for someone who had the
pure stuff.

I do have one question: is this the appropriate way to titrate with
methyl orange indicator? Are these calculations right?

The only other problem I see is all the grunge bits floating on my
etchant - I think this is the dissolved bits of the "airstone" I tried
until it mushed out. I'll try coffee filters to get rid of it.

I will be etching some boards eventually <g>. All this chemistry is
more than what is needed to use this approach, but I find it a fun bit
of learning. 

For anyone interested in trying this approach, don't let it scare you
off. The "quick, cheap and dirty" analysis mentioned on the website
(in the links) on Etching with Copper Chloride Etching Systems is
likely all you need. 

www.pacificsun.ca/~robert/pcb/pcb.htm

My next focus (I hope) will be trying to get a fairly even etch.

Grant