Homebrew PCBs

On Mon, 4 Jan 2010, jimofc300 wrote:

> Hi,
>
> While I'm an experienced design engineer, I've never done a PC board in 
> 40+ years of design. We had a special department to do that. Now 
> retired, I thought I'd try inventing. I find PCBs important to that 
> goal.
>
> In getting together a kit to do this, I had a few thoughts and 
> questions. I hope you more experienced (though not necessarily older) 
> and (presumably) wiser folks :-) can address some of these questions.
>
> 1)  I've looked into photo paper and "Press-N-Peel" to transfer toner as 
> resist. Do you think laser T-shirt transfer paper, which is probably 
> cheaper, would work, too? Has someone tried this?

Might be worth a try.  Lots of people have success with the slick pages of 
magazines.  The ink already there won't transfer and the clay will hold 
the toner just enough to let you do a heat transfer.  Look up "Gootee 
board" for the guy who came up with it.

> 2)  Do you think latex gloves, as you'd find in a doctor's office, would 
> be safe for handling boards and etchant? They're cheap at Walgreens and 
> disposable to reduce cleanup effort.

Those would work fine.  The biggest hazard with ferric chloride is that it 
stains just about everything including glass and skin.  So, think twice 
before you borrow your wife's cassarole dish for etching.  My custard cups
now have an odd tinge of yellow.

> 3)  If ferric chloride wouldn't destroy them, would kitchen plastic bags 
> (ZipLock-type) work for etching boards? They'd probably save on etchant 
> and, if I don't slop too much, reduce cleanup.

I never thought of that.  Maybe.  Another method to be stingy with etchant 
is to wipe the board with a small sponge or swab.  It takes a lot longer 
that way though.

> 4)  How nasty is used ferric chloride? Is it a HazMat material? How do 
> you folks dispose of it in an eco-friendly manner?

Small amounts down the drain is generally considered okay.  See also 
http://hackaday.com/2009/01/26/ferric-chloride-etching-chemistry/ 
for other ideas and alternative etchants.

> 5)  Would Krylon spray clear coating and/or spray paint work as a solder 
> mask? My thought is to spray the board immediately after etching and 
> touch-up. Then, I would assume, soldering would burn off the paint 
> instantly. Would a second coat be necessary after assembly?

You can do that, but it won't work as a soldermask because the heat of 
soldering burns off the film.  It'll do the other job of soldermask: 
keeping the copper untarnished.  Transparent Green Candy Apple by Testors 
gives something very close to the classic green soldermask and lets the 
traces show through.  A spray afterwards probably isn't necessary.


-- 
David Griffith
dgriffi@...

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