Hello Werner,
I agree with you, there has been significant progress in the area in the
last 30 years.
There has been many attempts at micro-mechanism based models for soft
solders, all with their own level of sophistication and limitations, e.g.:
1. Sandia's model (which predicts coarsening bands in SnPb joints extremely
well)
2. Huang's model (CHMT, Vol. 15,Aug. 1992) which is based on dislocation
motions and theoretically predicts that cycles to failure go as the inverse of
strain energy. This was then confirmed empirically by Huang et al. for SnPb
assemblies.
3. Wong et al.'s model (Hughes Aircraft, 1998) which uses a creep / crack
growth based approach for SnPb
4. The Syed approach (Amkor) also relies on creep fatigue mechanisms,
coupled with empirical correlations of ATC data.
Other names that come to mind for micro-mechanisms based approaches include:
Pr. Basaran and their students, Pr. Keer and Fine of Northwestern and their
students (Mavoori etc...) ... and a few others.
There are also engineering approaches (Coffin-Manson or strain energy based)
which seem to work fairly well for SnPb, and now for SAC assemblies. See my
list of 12 SAC models in my SMTAI'05 paper - which can be downloaded from my
web page. There was also a very interesting paper on a crack growth based
approach by Paresh Limaye (IMEC) at SMTAI'05, with an excellent correlation to
SAC empirical failure data.
Each and every model has its own merits and limitations and it' s up to the
user to decide whether a given model is appropriate or not for his/her
application.
There is always room left for improvement and I am looking forward to new
developments in the field, including more micro-mechanism models.
All the best,
Jean-Paul
In a message dated 11/16/2005 12:12:35 PM Eastern Standard Time,
[log in to unmask] writes:
I respectfully disagree--I have been at this for some 30 years--and I KNOW
it
works. The reliability of the solder attachments can in fact be estimated
depending on the various physical parameters.
Quote of the month:
"I often say that when you can measure what you are speaking about, and
express it in numbers, you know something about it; but when you cannot measure
it, when you cannot express it in numbers, your knowledge is of a meagre and
unsatisfactory kind" Lord Kelvin
_______________________________________________
Jean-Paul Clech
EPSI Inc., P.O. Box 1522, Montclair, NJ 07042, USA
tel.:+1 (973)746-3796, fax: +1 (973)655-0815
_http://www.jpclech.com_ (http://www.jpclech.com/)
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