Terry, The question should be is why are you recieving boards with intermittent opens from your board manufacturer. It sounds like there is a serious design or manufacturing flaw with this particular board. Are the opens in same location of the board or are they random throughout the board? Tony Steinke AIT-Atlanta Inc. ----- Original Message ----- From: "Terry Exell" <[log in to unmask]> To: <[log in to unmask]> Sent: Monday, July 15, 2002 11:45 PM Subject: [TN] Stress screening of multi layer production boards for optimum reliability > 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 > -------------------------------------------------------------------------- ------- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------