What has surprised me is that no-one has suggested ways of avoiding to have to bake the
boards. Epoxy which has absorbed moisture has a Tg reduced by about 20 °C and some of
temps suggested here will take some types of  boards above their Tg and this is BAD.
Doing it twice in 48 hours is WORSE. Has no-one ever thought about specifying that the
suppliers of the board (especially high value-added M/Ls) ensure that the humidity is
never more than, say, 0.1% of the epoxy weight and that they be packaged in such a way
that they will keep that way for six months minimum? Then they won't need that
expensive and artificially aging bake under poorly controlled conditions which cannot
enhance the reliability of the finished product. And, yes, it can be done. The company
I was working for at the time guaranteed solderability and no blow-holing for 6 months
over 30 years ago. The FAB industry has perhaps conned the assemblers into accepting
second-class products which require treatment. Or rather, the assemblers have conned
themselves into thinking that baking is normal.

That should put the cat among the pigeons :-)

Brian

Rick Thompson wrote:

> I'm trying to establish some basic guidelines for the baking of bare PCB's
> that have potentially absorbed moisture due to unknown storage conditions
> and time.  Are there any industry guidelines for this type of process or
> would someone mind sharing their general procedures?  I thought I had read
> somewhere about times in the 2-8 hour range at 125 C but can't find that
> information anywhere.
>
> Thanks in advance.
>
> Rick Thompson
> Ventura Electronics Assembly
> 2665A Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858 voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
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