Hi Bev, A crack is a crack is a crack--even a micro-crack. So what does that mean? As I said: "Solder exhibits micro-voids at grain boundary intersections after about 25 to 30% of the fatigue life having been consumed, and micro-cracks along grain boundaries after about 40%. That means about 60% of life is still available when 'observable' micro-cracks are present." These micro-cracks are only 'observable' in cross-sections under the microscope. Prior to the micro-voids, grain coarsening is 'observed.' As the fatigue loading continues, the micro-cracks grow, and coalesce, becoming macro-cracks until a continuous fracture makes the SJ separable. In all this time the SJ will be electrically conductive [in the later stages high frequency signals may experience rise-time degradation, however]. However, the strength of the SJ will continuously decline during the process of accumulating fatigue damage. "How big of a crack in thermally cycled solder joints is too big of a crack?"--you must make that determination for yourself depending on your application. Werner Engelmaier --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------