Homebrew PCBs

Hi Chris,

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
<lcdpublishing@...> wrote:

> I guess what I am saying is this.  The next time you get "Missed 
> spots" with toner transfer, take a really close look at that area on 
> the copper to see if it is in fact flat and smooth.

I've been using a green Scotch Brite type of scrubber for decades and
that has worked fine for me.  I've used ruby tape (red adhesive tape),
rubon transfers, Sharpie marker, and now toner transfer.

I scrub the board in one direction until the surface looks clean, then
I rotate 90 degrees and do again.  I finish off with a cotton swab and
98% IPA and let the boards air dry.

When I have problems with toner adhesion, it's usually because there
was some dust or lint on the board.  Another source could be some oily
residue left on the board during the cleaning process.

The Scotch Brite cleaning method has been well documented and widely
used by many with no prolems.

If you're having adhesion problems, make sure it's not because the
board is dirty or you're not applying enough heat.  The two problems
I've had are dust/lint and insufficient heat.  When you're using the
paper transfer method, you can't see this as your transfering.  I use
inkjet transparencies and I can see the problem areas as I'm ironing.
   With transparencies, I can see areas that don't seem to be melting
enough and I can selective apply more heat/pressure to those areas.  I
can also see when areas are getting too much heat and avoid them.

Apparently there's a gelatin type of coating on the injket
transparencies that makes it easier for the transparency to release
the toner after ironing.  With inkjet transparencies, I heat the toner
enough to see visible (but not bad) toner spreading/melting.  Then I
let things cool to the touch, but may still be warm.  Then I peel the
transparency off.  On rare occasions, I didn't apply enough heat and
toner is staying on the transparency.  In those cases, I stop peeling
as soon as I notice a problem and apply more heat.

Toner adhesion doesn't have to be as good as you'd think.  I had a
case where some toner lifted during etch and bridged two adjacent
traces.  When I finished, there was a copper bridge that I needed to
remove.  I could have etched the board longer, but it was only that
one area that needed more etching and etching the whole board would
have caused over etching on everything else.

Regards,
Dennis