Hello TechNet,

Has anyone had any success predicting, measuring and correlating solder fatigue wearout for circuits that are continuously ramping up or down in temperature (linearly) between fixed thermal limits over fixed time periods? The fixed time periods are stable and repeatable as is the temperature change over these periods. 

As an example, a normal ramp-up time is 30 minutes and the temperature ramps linearly from 20C to 40C. Then the temperature immediately ramps down from 40C to 20C over the next 30 minutes. This pattern repeats.

The Engelmaier method described in IPC-D-279, IPC-SM-785 assumes cyclic temperature swings between two fixed temperature limits.  The solder joint temperatures stabilize at each temperature limit for a fixed interval before periodically switching to the other temperature limit for the same interval.  How can be solder fatigue wearout be quantified in solder joints that instead of “soaking” or stabilizing at each of the temperature limits, are always either heating up or cooling down between these known limits in a predictable, linear way?  Intuitively, it seems that creep and stress relaxation should be less, but how to quantify when solder joint wearout occurs (N50, mean lifetime)?

Thanks.

John Nieznanski
 


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