Pratap,

I would caution the use of your equation without further information
about the use environments and design conditions.

The exponent you cite is actually the negative inverse of the plastic
fatigue ductility exponent as defined by ASTM fatigue standards.  If
the PCB design and use environment induce plastic strains in the
solder joints than your equation may be valid.  But, if the design and
use environment do not strain the solder joint enough to cause plastic
strains (i.e. the design induces elastic strains) than you must
consider an elastic plastic fatigue model for comparing the damage.

In other words, your test condition is probably causing plastic
strains while the use condition may cause elastic strains.  Using a
purely plastic fatigue equation to compare the damage between the two
conditions may give very misleading results.
--
Karl Sweitzer
Eastman Kodak Company             voice: 716.47.77546
800 Lee Road                        fax: 716.47.77293
Rochester, NY 14650-3118         mailto:[log in to unmask]

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