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

(The first part is not my question -- just an account of my success
with fabbing a PCB. Skip to the asterisks to see my real question.)

First off, thanks to everybody on this group and all the data thats
been accumulated here. Last night I gave my first go and doing a
toner transfer board and it went pretty well. My first try was with
Office Depot photo paper, which didn't work at all. Then I ran out to
Staples before they closed and got their glossy photo paper, it was a
dollar under list price. The paper worked great and it took about 15
minutes to go from plain board to transfered design. Then I mixed
some Ferric Chloride from Datak powder and etched the board. I didn't
heat the etchant but it was still pretty warm from mixing and took
5-10 minutes to etch. For the first few minutes I just let it sit
while I was busy doing something else, without much effect. Then I
took a balled up paper towel and rubbed the board, not hard but
pretty vigorously. This was a great way to do it, because it let me
focus on the areas that needed it (around thermals the etchant was
slower to work) without leaving the board in there so long that it
undercut the traces. This morning I mixed up some Datak Tinnit and
tinned the board. I don't have all the components yet but I did a
solder a 20-DIP socket, v-reg, and a few capacitors to the board. It
all went really well. I think my next one will be even better.

∗∗∗

Anyway, this all has made me curious about the chemistry involved in
etching and tinning. Namely, what exactly is Ferric Chloride, and how
does it react with copper? I think its FeCl3, and it reacts with
copper to make some sort of cupric chloride, but I'd really like to
know the exact chemistry involved, if possible. Especially, what's
left over after the board is etched, and what hazards do those
chemicals represent?

Also, does anybody know how Tinnit works? It smells kind of bad,
almost like sulfur...I just want to know what kind of chemicals I'm
dealing with, how dangerous they are if they spill, evaporate, etc.
Right now everything is stored in glass jars with plastic lids and
clearly marked labels. In the case of the etchant, the jars are also
labeled with "POISON" and a skull and cross bones and stored safely
in the garage. No kids live here.

Finally, whats the best way to clean up after I'm done? The etchant
and Tinnit are both acids, so it seems adding a base (like baking
soda) would neutralize the acid, and then I could wash off in the
utility sink in the garage. (Stains aren't a problem down there.) I
haven't done that yet, because we do have copper pipes and I don't
want to do any damage to the house. Notice I'm only talking about
washing off in the sink, to dispose of the used chemicals (which I
poured into separate jars in the hopes of reusing), I was planning on
adding dry baking soda to both neutralize and solidify the etchant,
then scooping it into a sealed plastic bag and putting it in the trash.

Thanks! Great group here!
Mark