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Date: | Mon, 11 Sep 95 10:28:40 EST |
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I agree with the first answer, provided the PCB is assembled in a
timely fashion. If not, then proper storage conditions are essential
to protect the subassembly from absorbing moisture. Some materials
can absorb as much as .2% moisture. This could lead to excessive
expansion when subjected to high thermal excursions.
I've always suggested a pre-bake (on parts that exhibit any issues
during assembly or for parts that have been placed in stock for
extended durations) of 15 minutes per layer at 150-210'F. (This
temperature is dependent on what type of components are on the PWA
already and if so, what type of temp rating they have.)
I know that for high layer count that the bake time could appear
ludicrous. But these high layer counts tend to absorb the most
moisture and exhibit the most issues.
______________________________ Reply Separator _________________________________
Subject: PCB Pre Bake
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 9/8/95 3:31 PM
If you buy a good quality board you do not need to bake the board. If your
problem is out gassing increase the through hole plating to a minimum of 25um.
Should be between 30-35um. If the problem is delamination the problem is the
bonding or the pre preg.
Bob Willis UK
Tel 01245b 351502
Fax 01245 496123
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