Dear All, I am experiencing occasional open circuits on 16 layer boards during assembly and during in-service use. I have started thermal stressing all production boards with the aim of screening out any boards with latent defects and this is identifying and removing some problem boards. However, an equal number of problem boards still fail during assembly. Does anyone use similar thermal stressing of production boards to help improve assembly yields and product reliability? If so, do you find it successful? 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. 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. My board manufacturer has made several process improvements over the last year but I have not seen a significant improvement in my assembly yield. Best regards Terry Exell PCB Assembly Engineer BAE SYSTEMS Plymouth, UK ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------