In a message dated 02/04/99 21:44:38, you wrote: >Would it be so severe in normal ambient cycle Werner ? >Even 90'C span over 24 hours seems (likely mistakenly?) pretty mild ? >I came across this as well ; >is there any average daily span ? in say average Alaskan warehouse ? >Could you elaborate a bit also on that 20'C cross line significance I noted >in the 785 standard ? >Could it be said storage forms equal part of the product life & warranty >considerations ? >Paul Klasek >http://www.resmed.com. Hi Paul, Well on the real ambient cycle I have of course no idea, but long-term storage at -50C would imply some more exotic locale. AT&T did some study many years ago for their outside-plant equipment and came up with a dailt delta-T of 35C as beeing representative of its customer base. What that means for Alaska or Spizbergen or Kamtschatka I do not know. In IPC-SM-785 the 20C demarcation temperature comes from the fact that above this temperature you have creep-fatigue low-cycle fatigue (LCF) dominant and below you have creep no longer dominant and solder behaving more like a structural metal including the build-up of stresses on loading. This has been shown by work of Roger Wild at IBM and Peter Hall at Bell Labs; thus, cycling through this temperature (it is of course not exact) means you are confounding two (and perhaps more) different damage mechanisms. This makes correlation difficult if not impossible and that is why the old MIL-cycle of -55 to + 125C is not a good accelerated reliability test. 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 ################################################################