4.4 NUMBER OF THERMAL CYCLES
In the past, the number of thermal cycles has varied from a low of 2 to a
high of 168. The number of cycles was selected based on module complexity.
Authorities now agree that a number of cycles should not be based on parts
count, i.e., complexity, but on the thermal parameters associated with the
hardware being screened.
NAVSEA’s approach to establishing the required number of cycles for a
particular TCSS program is to establish a lower limit on the number of thermal
cycles, and increase the number of cycles based upon:
Reduced rate of temperature change
temperature range (T)
Reductions in temperature range and rate of change are necessary when the
equipment is unable to withstand the larger T or the thermal cycling
equipment is unable to change the temperature rate as quickly as desired.
A reduction in the number of thermal cycles may be justified if screening
data demonstrates that an insignificant number of latent defects are
stimulated after a certain point when TCSS is performed in accordance with the
requirements of this document.