Paul

I'm against heat sealing polyethylene (PE) or any plasticised bag with PCBs or PCAs
inside. I made tests about 30-35 years ago and found that the heating was sufficient to
evaporate both the plasticisers and (in the case of pink bags) anti-static compounds.
These are both hygroscopic materials and will condense, albeit in small quantities, on
the contents. Low temperature (35°C, 95% RH) SIR tests will reveal the potential harm.
Above 50°, an SIR test may not reveal it, as the stuff may evaporate from the board
during the ramp-up.

In any case, what's the point of sealing PE which is as porous as a sieve, anyway?

At the time I did these tests, we were looking for a packing material for bare boards
(M/Ls) which was 'opaque' to all forms of external contaminants and exempt from
internal ones. We settled for tri-ply food bags with a very thin polypropylene layer on
the inside, Sendzimir-rolled aluminium foil outside that and a thicker polyethylene on
the outside, to give robustness to the other two layers. This would vacuum heat-seal
perfectly and keep the PCB solderable with just a Sealbrite coating on a specially
treated copper for five years. Nothing could get through the aluminium.

This doesn't answer your question, but may be of interest! :-)

Brian

Paul Klasek wrote:

> Dear Forum
>
> Would anybody have any good, bad & ugly tales of belt sealers :
> insert filled bag , slide into dual belt , let fly through sealing heated
> roller ,
>
> as comparing to timed solenoid clamped dual (bottom and top) heat strip
> press sealer ?
>
> Application is medical kit pouch, not sterilised .
>
> thanks a lot                 paul
>
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