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 ##############################################################