Hi Vladimir, All fatigue models, not just for solder, are empirical models. Because no such model can take into account all possible variables, they concentrate on 1st-order parameters, and some 'adjustments' for 2nd-order influences. The Coffin-Manson model is empirical, and even a simplification of the more comprehensive, but still empirical, Morrow model--both of these only take into account fatigue from plastic deformation (low-cycle fatigue). The Basquin equation is empirical--taking into account only fatigue from elastic deformation (high-cycle fatigue). In the early days of fatigue studies [and early days lasted into the 60's], nobody even dreamed of using material in cyclic loading that was high enough to cause plastic deformation (yielding). Both of these models are only for non-creeping metals. The Engelmaier-Wild model, and others for solder, take the plastic deformation resulting from creep into consideration. If you combine the Coffin-Manson and Basquin equations, you wind up with something like the Engelmaier model on which ASTM E 796 “Standard Test Method for Ductility Testing of Metallic Foil” and the modeling for both flexible circuitry and plated-through vias are based. I am certainly aware that 'scientists' have been bothered by the fact that fatigue models cannot be developed from first principles--but I rather have empirical models than a repeat of the 'Comet' jet liner disasters. The difference between 'scientists' and 'engineers' is that the latter have to make decisions and build product based on incomplete information. Regards, Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 -----------------------------------------------------