Hi Terry, >My thermal stressing uses the following parameters: >10 cycles of hot / cold exposure in a HALT chamber, >-60 deg C to +120 deg C temperature excursions, >40 deg C per minute temperature ramp rate. >The boards are electrically tested after thermal stressing. A: The ramp rate surely is not correct. What exactly is a "HALT" chamber? Depending on the nature of the failures you experience, your testing is not much of an ESS, and electrically testing after, not during, thermal stressing will show little even if latent defects are precipitated to failure. >I calculate the screening is using approximately 20% of the expected life of the >assembled boards, so I am reluctant to increase the stress levels. A: On the basis of what model do you make this calculation? You do nopt even have a failure mode, let alone a root-cause failure mechanis. >My board manufacturer has made several process improvements over the last year but >I have not seen a significant improvement in my assembly yield. A: Again. without knowing what is really happening, what the design details are, and how these PCBs are used, it is impossible to make concrete recommendations. 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 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 ---------------------------------------------------------------------------------