Hi Al, No, you are not wrong. Many failures, excluding brittle interfacial failures due to some adhesion weakness, due to creep-fatigue of the solder are near-interfacial. That has 2 underlying reasons 1) many solder joints have their smallest cross-section near the interfaces, particularly solder balls, resulting in much higher loading near the interface, and 2) near the interfaces the solder alloy is somewhat depleted of Sn used up in the formation of IMCs, and there is evidence that solder alloy with an abundance of Pb-rich phase [sorry, no data yet on LF-solders] has less fatigue resistance. So, your FEA model does not need to include the IMC layer(s), but in order to do what you are aiming at, you need the properties if the near-interfacial solder alloy—good luck with that! Werner ************** Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------