We have been debating the proper dwell time for thermal cycling tests. Per
IPC-SM-785 it should be 15 minutes (min.). Indeed the majority of
publicized thermal cycling tests use dwells of 10-20 minutes. However,
there are camps that advocate longer dwells (min 30min.) to sufficiently
account for the effects of creep fatigue in solder joints.

What rational/assumption was used for defining the minimum dwell time for
space applications in IPC-785?  Would longer dwell durations significantly
change the cycles-to-failure results? What factors would have to be
considered to assess any compromises?

For reference, our target application is space-borne. Thermal cycling
extremes are -55C and +125C. CTEs between parts & PWB will be matched to
<5ppm/C difference.

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