Hi Ingemar [do you ever sleep?],
Yes, FEM models can get quite large, even when you take advantage of the
8-fold symmetry. But your problem does not stop there, because the out put is just
the location(s) of highest stresses and strains where failure(s) will
initiate together with some highly localized stress and strain values. Now, what is
it you do with this information? How do you translate that to cycles-to-failure
at what failure probability?
And as I said earlier, the MTBF concept does not apply to solder joints [or
any other wearout situation, for that matter. Why, you might ask? Visualize the
Reliability "Bathtub" Curve with its 3 regions of 'Infant Mortality' [with
deceasing failure rate, 'Steady Operation' with its assumed constant failure
rate, and 'Wearout' with its increasing failure rate. The MTBF concept works fine
for the constant failure rate 'Steady Operation', the problem is that solder
joints fail in 'Wearout' where the rapidly increasing failure rate is making
the MTBF concept invalid.

Werner

---------------------------------------------------
Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------