I was asking about Component Failure Temperature a few days ago and had
some very useful replies, as ever, for which many thanks to all who
contributed,  but Francois Monette led me on to the topic of Moisture
Sensitivity. As far as I can see, all the specs and information only
consider moisture absorbtion of MSD's up to the point of soldering and not
beyond. The obvious concern is that of internal weakening of the devices,
delamination or pop-corning at soldering temperature, as that's
catastrophic. The more insidious after effects maybe aren't important
enough yet to warrant much attention.

I presume that MSD's continue to absorb moisture after they are soldered,
especially when subjected to those awfully nice water wash plants (for us
non-no-clean types). Is there any information or studies, that anyone knows
of, that show how post-soldering moisture absorbtion affects component
performance under operating conditions, especially if the boards aren't
conformally coated? Does all that water getting into the boundary layers of
the guts of a component not have some significant effect?

What, too, if boards have been conformally coated after being washed, but
not pre-baked to remove absorbed moisture. Is it trapped in there, or does
it dissipate and, in doing so, does it affect the coating? I haven't heard
any recommendations yet about baking boards prior to coating. Has anyone
else? Or have I been kept in my box too long and the world has passed me
by?

It will be interesting if this posting generates a lot of debate. Or
embarrassing if I'm being a numpty (Scottish expression).

Regards

Pete Duncan

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