I don't believe in models for soldering..
I'm a gaggy old dog that like hands on. I use to start tempcycling
and life tests immediately. Such tests do not tell the whole truth
either, but safer than models. Models tend to indealize terms and
factors, but reality is more like a mustang. Hard to catch, hard to
tame. A collegue here has developed a model for BGA solder joints, pages
and pages with math, and he is very ambitious and loves what he is
doing. We implemented his huge
model for some boards, but the result of the simulations was so
diverging and indistinct that we couldn't figure out what could be
presented to our customer. I think the problem lies in the very invidual
characters of solder joints, like leaves on a birch..all are different
even if they look similar.
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Werner Engelmaier
Skickat: den 16 november 2005 16:49
Till: [log in to unmask]
Ämne: Re: [TN] [LF] Reliability prediction of LF soldering
Hi Ofer,
I certainly know what MTTF and MTBF means, and for some things these
concepts
work--MIL-HDBK-217 was built on them. However, for solder joints this is
different and that is why MIL-HDBK-217 does not work for solder
attachments.
Solder joints are not equally loaded [the one's on the corners see
significantly more loading, everything else being equal]--that is why
one always deals
with all the solder joints on a component. The solder joints on various
components have different loading conditions as well depending on
component size,
solder joint geometry, and component power dissipation. The life of a
compont's
solder attachment [all solder joints] is measured in terms of cycles not
time
per se. That is why reliability models need to exist to determine an
estimate
of the fatigue life of the solder attachments. There have to be
different
models for leadless and leaded solder joints [here lead has nothing to
do with Pb]
and different models for different solder alloys. We simply do not have
the
data at this point for Pb-less solders to develop fatigue reliability
models.
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
-----------------------------------------------------
---------------------------------------------------
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
-----------------------------------------------------
|
