Hi Werner! Terry is describing a HASS (highly accelerated stress screen) or a HALT (highly accelerated life test) type of chamber. We have six of the HASS chambers which are used to improve printed wiring assembly design robustness (we track what fails, determine if that failure mode/mechanism is valid for the use environment and make any appropriate design improvements). These chambers can indeed provide temperature ramp rates of 5-50C per minute (they use LN2 boost) - the ultimate in thermal shock recipes. I think you raised the most important questions - what is the relationship of the failure modes/mechanisms induced by the HALT chamber and the failure mechanisms the printed wiring assembly undergoes in its use environment? Pretty tough question. Dave Hillman Rockwell Collins [log in to unmask] Werner Engelmaier <[log in to unmask]>@ipc.org> on 07/16/2002 07:25:49 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to [log in to unmask] Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: Re: [TN] Stress screening of multi layer production boards for optimum reliability 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 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------