Hi Richard,
Certainly shooting something lke a electronic proximity fuse out of the
barrel of a gun generating about 50,000 g's, creates a lot of forces. On the other
hand, most of these items are used after years of storage in uncontrolled
environments where SJs experience thermal cycling and accummulate creep-fatigue. I
have seen instances of such failures for SJs without voids; voids certainly
would not help things under those circumstances. But with a full damage
mechanism/root cause analysis, we are still at the conjecture level. [If you are so
inclined you may want to take my Root Cause analysis workshop in
December--e-mail me for details]. In this case it that component hole could have prevented
proper wetting--you say "One of these [1208 capacitors] ... actually ... came
out of its solder joint on one end."
I have seen BGA SJs with voids fail but also BGA SJs without voids--in some
of these cases the SJ right next to it with a void had not failed.
No the story about void actually improving is a myth created by
misinterpreting some of the initial void work by Chuck Schmidt at SRI. He reported, that a
void retarded the crack propagation in its direct vicinity, but not away from
it. Once the crack front passed the void the retarded portion of the crack tip
caught up rapidly--thus, no reliability gain.
The voids that could be a problem are the ones in the solder balls of an
unsoldered component--it means less solder volume, and thus could lead to lower SJ
height and therefore reduced reliability.

Regards,
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, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com

---------------------------------------------------
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
-----------------------------------------------------