Werner, Well said! Now is anyone listening! David A. Douthit Manager LoCan LLC Werner Engelmaier wrote: > Hi Howard, > I have never seen: Spec Number TSC7514g, section 5.4, reference specification > TSC 7010g, or anything like it, and I have been involved in SMT reliability > for almost 25 years. > >The first question is: is this customer using their own test or is there an > >IPC test for thermal cycling of a completely assembled circuit board? > ANSWER: The test (Ts, dwell times) is reasonable, except for its use of > thermal shock--T-shock will give you totally misleading results, because the > high T-gradients cause component and PWB warpage, and thus create tensile > loads not seen in product. Further, a different damage mechanism in the > solder [see Günter's response] occurs due to the much higher stress levels > occurring with T-shock. For test guidelines and a standard go to IPC-SM-785 > and IPC-9701. > > >The second question is: is the customer's temperature range too extreme, > >which is causing severe thermal shock, which is then causing joint failures > >due to different co-efficients of expansion and contraction (board, solder, > >lead)? > ANSWER: For T-cycling, the Ts are not extreme. For T-shock the differences in > CTEs are not as much of a factor as are the T-gradients. > > >The third question is: is the use of 3,500 hours of thermal cycling realistic > >and/or too long? > ANSWER: For T-cycling no--all bets are off for T-shock. > > 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], Website: www.engelmaier.com > > --------------------------------------------------- > Technet Mail List provided as a free 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/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------