Peter, thanks for the wake up - you're absolutely right. Except for the occasional house cat knocking a VCR off the TV while prowling, our's is a very benign environment - normal household. Bob Croslin Nielsen Media Research -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Wednesday, October 16, 2002 8:50 PM To: TechNet E-Mail Forum.; Croslin, Robert Cc: [log in to unmask] Subject: Re: [TN] Stacking of components (SMD) Revisited Stacking components is definitely taboo for high reliability boards, especially those operating in conditions of vibration. The additional and offset mass of the components / shift in C of G puts extra strain on the main component-to-board solder joints that is undoubtedly detrimental to the (long-term) reliability of those solder joints, and maybe the capability of the component materials themselves (CTE differences in unusual configurations may cause ceramics to crack). Stacking is probably fine, though, for TV's VCR's, PC's, etc that normally operate in a benign environment, so as usual, "it depends" on the application and the nature of the stacking (how many, how high?). In theory, the definitive answer you want is "it is detrimental to reliability". In practice, though, how detrimental is impossible to say, as it will be proportional to the components involved, how they're stacked, the operating conditions, how the equipment is used, the processes involved to make the board, the characteristics of the board, where on the board the components are located, how the board is fixed to its chassis, the charateristics of the chassis at that / those point(s) .... you get the picture. Reliability comes down to experience and data collection for the particular equipment and stacking configurations you have in place. I suspect the best you can hope for is any stories of failures (if folks are prepared to tell them) of stacking configurations that regularly fail regardless of equipment type and operating conditions Good luck! Peter "Croslin, Robert" <[log in to unmask]> 16/10/2002 11:16 PM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to "Croslin, Robert" To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: Re: [TN] Stacking of components (SMD) Revisited Alex, we do it at Nielsen on a regular basis because we have to mutate our equipment so regularly. Imagine the possible combinations of TV's, VCR's, and set top boxes nationwide that we have to meter to gather the data we process into the TV ratings. We've been stacking, book ending, and building little Stonehenge like structures out of R's and C's for years with no apparent effect on product reliability. We do it both in our repair lab and at our external subcontract manufacturers. While I have no hard data, we simply don't consider it an issue. Hope this helps. Bob Croslin Nielsen Media Research -----Original Message----- From: Alex Krstic [mailto:[log in to unmask]] Sent: Tuesday, October 15, 2002 3:48 PM To: [log in to unmask] Subject: [TN] Stacking of components (SMD) Revisited Hi all. Well I have gone through the archives hoping to find the "definitive" answer to no avail. Does anyone have quantitative reliability data on stacking of SMD components? All past discussions end in the conclusion that you can do it but don't do it if you don't have to. Alex Krstic NovAtel Inc. ---------------------------------------------------------------------------- ----- 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 ---------------------------------------------------------------------------- ----- --------- [This e-mail is confidential and may also be privileged. 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