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This is the board before tin plating. It's a small power supply
board, with 12v in, and 5v linear and 3.3c switcher regulators. I
scrubbed it bright and shiny with a green scrubbing pad and some dish
soap, then dried with a paper towel.
This is the setup I'm using. I have a 4oz bottly of MG Liquid Tin,
and an old hard drive shipping clamshell. The clamshell is plastic,
and just the right size for this procedure. Note that I'm using a
bench that's used to being chemically abused.
The 4oz bottle gives me about 1/4 to 3/8 of an inch (half a cm) of
fluid, easily enough to cover the board. The board starts changing to
tin colored in a few seconds, but it takes the full 3-5 minutes to
make sure it's fully covered.
The results, after rinsing and drying. Note that the covering is not
100%. This could be due to poor cleaning, but I tried leaving it in
longer and the coating became dark grey and messy. (Note that other
times since then I've left it in longer without it getting messy,
YMMV)
Now with a silkscreen layer added, again with a simple toner transfer.
Note that the toner didn't stick where there wasn't any copper,
because those spots are "deeper" than the copper and there wasn't any
pressure there from the laminator. It stuck to the tin just fine,
though.
Finally, with all the parts soldered on. Some of the through-hole
parts are on the other side, like the power connector and
electrolytics. The 7805 is on the top because it's easy to solder
that way.
Both reflow solder (
via hotplate) and hand
soldering seemed to be unaffected by the tin plating.
Don't touch the tin coated surface until you've rinsed and dried
it. It seems to be easily wiped off when it's "fresh". I did this
the first time through, and had to re-clean and re-coat the board.
The coating is very thin and can be removed with a green scrubbie,
although this leaves a black stain on the scrubby (I have a separate
one I use for chemicals).
The odor is hazardous and very unpleasant. You definitely want
good ventilation when using this. The chemical itself is otherwise
clear, like water.
