Hi Sarah, >1) Q: what is the difference between IL separation and post separation? A: Post separation is the old, and now obsolete, term for innerlayer (IL) separation. >2) Q: what causes the occurrence of such kind of defect? A: The compressive forces on the PTV barrel from the hydrostatic pressure generated by the thermally expanding resin forces the PTV barrel to plastically deform (buckle) inwards. On cooling, the now shrinking resin retracts, causing tesile forces on the PTV barrel and the innerlayer interconnects. This causes separation of the barrel from the resin and not infrequently, IL separation. Il separation is aided by the land roation of the innerlayer lands due to the movement of the expandingresin in the z-direction. For this reason, IL separations are primarily found in layers 2, 3, N-1, and N-2. The cause of IL separation is the same as for PTV barrel cracking; what fails first depends on which is the weaker link in terms of both quality (drilling, smear removal, etchback, plating thickness/foil thickness balance, copper properties) and load distribution (hole size, PCB thickness, Tg, Tmax, T-gradients) >3) Q: how can we prevent this type of problem from occurring? A: Limit the maximum temperatures experienced by the PCB (worst offender processes are manual soldering/rework operations), limit the number of all soldering thermal excursions (HASL, reflow, wave, manual soldering, rework/repair), use high Tg resins, use E3 copper foil, avoid thin innerlayer Cu foil with thick barrel plating (balance). >4) Q: at what layer does this problem usually occur? A: IL separations are primarily found in layers 2, 3, N-1, and N-2; PTV barrel fractures near the center of the PCB. >5) Q: how can you distiguish separation from resin smear? A: With great difficulty, if at all. But resin smear only causes IL separation at the foil/electroless Cu interface; IL separations can also occur at the plated Cu/electroless Cu interface and in the IL foils near the IL interconnects. 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] ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################