Hasan, I agree with the flags you raised about various FEA approaches. Another issue is that the correlation of test data has a strong dependence on element size (this was demonstrated with hard data and careful studies by R. Darveaux at SEM'96). This may not be a problem when you model similar joints and do parametric studies on package and board variables alone. However, the FEA approach becomes an art when you have to deal with joints of different sizes, as in flip-chip vs. QFPs vs. BGAs. You then have to use consistent element sizes from one model to the next and make sure that element sizes are somewhat the same as in the FEA models that were used to develop a correlation of test data. These problems arose on top of the singularity issues that you mentionned. Also, because of long run-times and high computational costs ($25K+ a year to lease a commercial code that handles plasticity and creep well - we don't get discounts in industry), most of us can't afford experimenting with mesh sizes. The averaging techniques that you mention have helped alleviate some of the problems. However, since by averaging results over the volume of a joint, you have a single number (whatever is used for damage), you end up in a "1D" situation. My view and experience has been that hysteresis loops from 1D (plane or axisymmetric) engineering models provide sufficient information to capture main effects and make a first order reliability prediction. (see my home page below for more info on how this approach was implemented). First order predictions are satisfactory for day-to-day engineering purposes (in general). This may also be the best we can do since we deal with a fatigue situation with joint-to-joint, board-to-board and product variability. I'll be looking forward to your reports on improved FEA approaches at INTERPack'97. With best regards, Jean-Paul ________________________________________________________________ Jean-Paul Clech EPSI Inc., P. O. Box 1522, Montclair, NJ 07042 - USA tel: +1 (201)746-3796 fax: + 1 (201)655-0815 Home page: <A HREF="http://members.aol.com/Epsiinc1/index.html">http://members .aol.com/Epsiinc1/index.html</A> - click on the above or copy: http://members.aol.com/Epsiinc1/index.html __________________________________________________________________ *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************