Mike

The best one I've come across is a triply envelope: a very thin unplasticised
polypropylene on the inside (to provide heat-sealing without evaporating contaminants
onto the contents, like PE does); the middle one is a thin Sendzimir-rolled aluminium
foil (to provide perfect barrier for moisture and chemical contaminants: do NOT use
evaporated aluminium) and a thicker polyethylene layer on the outside to make it
robust. Vacuum-sealing a bare PCB in that will give you virtually perfect protection
and conservation. We used these for individually packing m/ls and had no blow-hole and
no solderability problems with just Sealbrite on the copper for years (both guaranteed
for 6 months, provided soldered within 48 hours after opening). This was 30 years or so
ago, when I was in charge of a PC fab shop.

The bags I describe are sometimes used for the long-term conservation of food without
freezing, where cans are otherwise unsuitable or undesirable for whatever reason.

Brian

"Mcmaster, Michael" wrote:

> There's been a lot of talk about baking and packaging boards to avoid
> problems from moisture sorption.  Does anybody have any recommended sources
> for moisture barrier packaging for PWBs?
> Mike McMaster
> RF Product Engineer
> Merix Corporation
> Forest Grove OR
> 503-992-4263
>
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