Charles-
Don't know where you are located but humidity will obviously effect
moisture absorption rates... here are some general guidelines:

1) Bake temp should be about 250 F.  Baking at less than 220 will do very
little to drive out moisture.  Extended bakes above 270 can embrittle the
adhesive.

2) Rigid-flex and flex printed wiring with acrylic adhesives are
significantly more hygroscopic than polyimide glass or epoxy glass
pwbs.

3) Profile ovens to determine start-up and recovery times - Large ovens
can take up to 10+ minutes to recover...

4) Standard flex single-sided / double-sided - 10-20 minutes
5) Multilayer flex (only) up to .050 thick - 1-2 hours
6) Rigid-flex 4-12 hours-- depending on thickness.

7)  After baking,  solder immediately - or use dry box with desiccant for
short term staging.  Thicker parts will absorb moisture more slowly.  Do
not recommend dry nitrogen.

Hope this helps...


>>> Charles Barker <[log in to unmask]> 07/19/99 11:25am >>>
Gosh Guys and Gals;

Are we the only ones working with rigid-flex? Or is this information
proprietary?  The responses have been less than usual for some
reason. Is
the server getting this out to everyone?

Thanks,

Charlie B.


---------------------- Forwarded by Charles Barker/US/I-O INC on 07/19/99
02:07 PM ---------------------------


Charles Barker
07/18/99 01:53 PM

To:   [log in to unmask]
cc:

Subject:  Board baking

We are just getting into regular assembly of rigid-flex boards. What are
folks doing about removing the moisture absorbed in the flex?

Is anyone using nitrogen as a drying agent?  What are sources of
"dry-boxes" and such?

All you flex makers out there, what do you recommend?

TIA

Charlie Barker

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