Homebrew PCBs

On Wed, May 14, 2014 at 7:01 PM, DJ Delorie dj@...
[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:

> That's because the tarnish is copper *oxide*, and as I mentioned
> earlier, HCl needs an oxidizer - so it etches the copper oxide but can't
> etch the copper.

Oh yes, it was exactly looking at the chemical reactions which
prompted me to try HCl as a board cleaner.

>  Be careful, though, HCl is a nasty chemical to work
> around.

Indeed, but less nasty than I had worried about.  One of the first
things I did was put a single drop on my skin to see just how nasty.
It did not really seem to do anything in the few seconds I left it
there before washing it off.  Vapors in the eyes and lungs, those I am
worried about.  Running a fan over the work area seems to take care of
that.

> Me, I use a green scrubbie.  Prepping a board for TT or UV is more than
> just cleaning the copper - you need to make a mechanically rough surface
> for the toner to cling, and the scrubbie does that.  Toner won't stick
> well (or at all) to a mirror finish (which is why it releases from
> transparencies).

Good to know.  I was trying it on some boards that I had already
etched, handled carelessly, and then let sit for a week.

> Unless you're doing fine-pitch surface mount parts, in which case the
> uneven surface of the solder messes you up a lot.

I can see where that would be a problem.  I am only *just* making the
jump from TH to SMD, and I'm starting with the coarsest pitch
components I can find.  It would certainly be possible to drag the
iron away from the pads on fine-pitch parts and leave them bare.

> Liquid tin is a lot easier to do, too, and you don't risk lifting the
> copper traces off the pcb.

I was worried about lifting traces too.  I tried to be pretty brutal
on my test boards and was rather surprised that I didn't lift any
traces.  I suppose this depends on the thickness of your copper and
how well it is bonded to the substrate.

I've read conflicting reports on the Liquid Tin.  Some people love it,
other people claim it provides little to no long-term protection for
your boards and doesn't really help with soldering SMD parts either.
One thing is for sure though -- it does make your boards look
beautiful!

-p.