Hi Ken,
Forget ESS! There is no effective ESS for internal PCB defects you can
perform on full assemblies without doing serious damage to the assembled part
and their solder joints. So whatever you do on any of them will either not be
effective or creates non-shippable scrap.
However, you do not say exactly what kind of problems you have with the PCBs.
"We have found some internal fab defect (cracking at one of the inner layer)
which we don't know is due to assembly process or fab process induced" does
not tell me very much. Where is the cracking? At the attachment of a layer
to a PTV near the PCB surface? [This would be innerlayer separation which can
come from a combination of bad E1 foil, out-of-control manual soldering, low
Tg dielectric, high resin content]

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################