Hello TechNet Gurus,

Using the classical IPC-D-279 methods, how would you determine SMT solder joint fatigue for the following situation?


 1.  SMT part turns on at upper system temperature limit (Thi= +50C), runs for 30 minutes at Thi+ = +70C, shuts off, part stabilizes at Thi= +50C for 30 minutes.
 2.  SMT part turns on at lower system temperature limit (Tlo= -50C), runs for 30 minutes at Tlo+ = -30C, shuts off, part stabilizes at Tlo= -50C for 30 minutes.
 3.  And now the twist, the system temperature can slowly vary between these limits as much as 10C in a 24-hour period.
 4.  How much fatigue develops after 50 thermal cycles between T-hi and T-lo?

Can I claim that the upper limit on fatigue can be calculated simply by running 50 operational cycles from the upper temperature limit (Thi= +50C to Thi+ = +70C)?

Can I claim that the lower limit on fatigue can be calculated simply by running 50 operational cycles from the lower temperature limit (Tlo= -50C to Tlo+ = -30C)?

Can I claim that the actual fatigue is somewhere between these two limiting cases (worst case, best case)?

Thanks.

John

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