The innerlayer failure you describe typically is the result of the z-axis thermal expansion mismatch between the copper PTH barrel and the PWB resin during soldering operations being too large for the interconnection to withstand. The actual failure mode (innerlayer foil, foil/electroless interface, electroless/electrolytic interface) will tell what is the 'weakest' link. The weakest link needs to be 'strengthened' or loading conditions need to be reduced; sometimes both. This subject is complex; I give a one- day workshop on the issue of design, manufacturing, and reliability of plated-through holes and vias. Werner Engelmaier Engelmaier Associates, Inc. Electronic Packaging, Interconnection and Reliability Consulting 23 Gunther Street Mendham, NJ 07945 USA Phone & Fax: 201-543-2747 E-Mail: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************