In a message dated 4/29/2008 4:19:24 A.M. Eastern Daylight Time,
[log in to unmask] writes:
I need to be able to predict the fatigue life of solder joints under
different thermal cycling and vibration load conditions. The PCB will
usually be FR4, the solder tin/lead, the components everything from
BGA's to chip passives. Ideally I need to provide an estimate on cycles
to failure.
While many of us on TechNet can help you some, I too do not think there is
exact empirical software.
Fortunately, you are using tin/lead where there is a lot more data, and
working models. I can give you the following personal observations from both the
IPC Relaibility Conference two weeks ago in Boston, and from our project
advising Crane Naval Depot on repair of interconnections in the face of the
lead-free avalanche:
1. Werner Engelmaier (and other consultants) can use projections from
fatigue equations to estimate first failure, assuming the input data is correct. I
am assuming you want estimated first failure, not some statistical
representation like when 10% failure or 50% failure. His presentation is posted from
that conference, but since it was for a fee by IPC, the presentation posting
on the IPC site is their property.
2. From our project analysis of many Weibull plots, we generalize that the
smaller the solder joint volume, the earlier the failure. BGAs and worse -
QFNs - are now getting a lot of publicity, because they are the first to fail in
thermal or vibration situations.
3. Vibration is a less exact science than Thermal cycle. What kind of use
condition are you dealing with? We are quite concerned about military
electronics in high vibration conditions where stiffer Lead-Free solders may be
used. Tests show that component location on boards is very important, as BGAs
can either be almost instantly failed, or can perform admirably, depending on
assembly location on a vibrating board.
4. FR4 is not always plain old FR4 in either thermal cycling or vibration
testing. Much of the newer, high temperature laminate is FR4, but has
different modulus and possibly even different moisture absorbsion, that effects
mechanical properties of the solder joints attached. Fortunately for Crane, most
military repair is on older 140 Tg boards that are not as stiff as the newer
laminate that can sustain highter soldering temperatures.
The prior recommendations for consultants and working consortia could be
quite helpful.
Dennis Fritz
SAIC, Inc.
**************Need a new ride? Check out the largest site for U.S. used car
listings at AOL Autos.
(http://autos.aol.com/used?NCID=aolcmp00300000002851)
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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
-----------------------------------------------------
|
