Sorry Werner,
I think I have expressed myself in my previous e-mails and to be honest with you, do not know what else to add.
Regards,
Vladimir
Vladimir Igoshev, Ph. D.
Senior Materials Researcher
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask]
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, November 16, 2005 1:11 PM
To: Vladimir Igoshev; [log in to unmask]; [log in to unmask]
Subject: Re: [LF] Reliability prediction of LF soldering
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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