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April 1999

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Subject:
From:
KELLY M SCHRIVER <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 9 Apr 1999 11:27:00 -0400
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Hi Bill -

Baking multilayer boards prior to soldering is a technique many of us adopted
in the late 1970's to "maximize delamination resistance".  This method of
removing absorbed water moisture was adopted after a considerable amount of
work with the old classic FR-4 with a ~110C Tg.  Baking was proven to restore
Tg on moisture laden boards - we used 125C for 4 to 6 hours.

You may want to sample some of your polyimide boards with TMA or DSC testing
to determine whether Tg is up to the manufacturers range for your specific
laminates.  If Tg is normal, then there would seem to be no reason to bake.
(I am assuming this is not an acrylic bonded rigid-flex.)

As an alternative to baking, you might consider having the board fabricator
package your boards in sealed vapor barrier bags (bulk quantities) immediately
after final cleaning & post-lam bake.  Keep the boards stored in the sealed
bags until just prior to assembly.

Got to remember, the additional heat cycle of baking is not going to improve
solderability, and it will, at a minimum, cost you the handling and process
labor.

Regards - Kelly

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