Hi Vladimir,
Which part of 
"All fatigue models, not just for solder, are empirical models. Because no 
such model can take into account all possible variables, they concentrate on 
1st-order parameters, and some 'adjustments' for 2nd-order influences.
The Coffin-Manson model is empirical, and even a simplification of the more 
comprehensive, but still empirical, Morrow model--both of these only take into 
account fatigue from plastic deformation (low-cycle fatigue). The Basquin 
equation is empirical--taking into account only fatigue from elastic deformation 
(high-cycle fatigue). In the early days of fatigue studies [and early days 
lasted into the 60's], nobody even dreamed of using material in cyclic loading 
that was high enough to cause plastic deformation (yielding). Both of these 
models are only for non-creeping metals. The Engelmaier-Wild model, and others for 
solder, take the plastic deformation resulting from creep into consideration.
If you combine the Coffin-Manson and Basquin equations, you wind up with 
something like the Engelmaier model on which ASTM E 796 “Standard Test Method for 
Ductility Testing of Metallic Foil” and the modeling for both flexible 
circuitry and plated-through vias are based.
I am certainly aware that 'scientists' have been bothered by the fact that 
fatigue models cannot be developed from first principles--but I rather have 
empirical models than a repeat of the 'Comet' jet liner disasters. The difference 
between 'scientists' and 'engineers' is that the latter have to make decisions 
and build product based on incomplete information."
do you disagree with?
We have been successfully been building product using these models since the 
'60's.

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


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