> No, no entropy change between us, we are pretty much of the same
> understanding I imagine. - but you may or may not be altering
> SolarWind's :-).
> I noted that you said "thermos" BUT that he said "EVEN an airtight
> lunchbox should do ..."
>=20
> So I addressed where he had got to and was going.
>=20
> You are of course correct about the thermos technically being a
> technically superior solution.It also has limitations which may or may
> not outweigh the gains compared to other alternatives.
>=20
> As I and others had noted, if you place the board in a sealed sub
> container you can then (probably) more easily control the RH of this
> smaller container. Both heating the container and/or  dehumidifying it
> with eg a Peltier cooler were suggested as alternatives.

I have to agree with Russell here. A thermos is good for only so long.
Eventually the inside of the thermos will reach the same temperature as
the outside atmosphere. The only way it could be better than a plastic
lunchbox is if it could be filled with dry gas - but then the lunchbox
trick can have the same dry gas fill.

Both could have silica gel or similar moisture absorbents put in them to
help keep the humidity level down.=20

But in some ways I would lean towards the plastic lunch box as it is
possible to mount the connectors in the walls of the box, and properly
seal around them. It is much harder to do that with a thermos as you
need to put the connectors in the stopper, or have a moisture proof
gland in the stopper. Either of these is going to be difficult for an
off-the-shelf thermos.

Another problem is the size of the thermos opening - it may put
unrealistic constraints on the size and shape of PCB one uses. You can
get suitable plastic boxes up to very large sizes, large enough that you
could have a 12V car battery in there with all sorts of electronics, and
still seal the whole lot up after a dry nitrogen fill, and know that it
is going to have a decent chance of not getting condensation inside the
box.
--=20
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--=20
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