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