DIYbanter - View Single Post - Repairing a TV remote control

On Wed, 15 Feb 2006 15:34:11 GMT, (GregS) Gave us:

In article , Roy L. Fuchs wrote:
On Wed, 15 Feb 2006 15:00:43 GMT, (GregS) Gave us:

I'm not sure that high octane alcohol is always needed. My point, as alcohol
dries, the water percentage goes up rapidly, attaining 0% alcohol
when it dries, and the remaining water accumulated from the moisturing
grabbing alcohol, stays around until it evaporates. Hot air
drying is almost always needed during the process.

greg

That depends on the temperature of the board AND the alcohol.

If both are warm, the alcohol will NOT leave any "dew" behind. It
will dry 100% , quickly and free of water.

IPA heats up in a microwave just fine. A small cup for 15 seconds
up to as much as a minute or so for about half a cup will get it very
near its boiling point. It also works much better as a solvent /
cleaner when it is hot like that, and evaporates nearly instantly.
I have set up many a production floor with vapor phase degreaser
machines using various solvent media.

Hot air drying is NOT "almost always needed" if one starts with
things in the right conditions to begin with.

If the PCB and assembly is hot, it will be pushing water OUT of it,
not absorbing it. Just make sure that it returns to room temp in a
dry box (ie the oven that got it hot). Not required though unless the
climate is VERY humid.

The last step should always be the half hour 120F bake out if one
REALLY wants all the water out of the hygroscopic PCB..

I have never thought od heating alcohol for obvious reasons, but
this may come in handy for stubborn cases. I had some boards
that the caps would absorb moisture or other stuff, and would
take days, months to dry without baking. I usually just
use a hot air pencil or gun to heat up boards.

Yet that practice is very dangerous. Even a toaster oven is safer
as it would heat the whole board uniformly (relatively). The pencil
is way too high a heat, and even feathered across the area desired is
a shock to the media, every time. Blow driers and heat shrink guns
can be used if they are kept far far away so that the heat has a
chance to cool a few hundred degrees as it passes thru the cool air on
its way to the target. Still the oven (toaster or otherwise) is
better. 120 F... 60 - 65 C.