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