The Reliability of Thermoelectric Coolers in Thermal Cycling Process (II)

High reliability and long life time can be achieved when the thermal cycling times is few, the temperature change range is narrow, upper temperature limit is low, as well as that temperature change is slow. On the contrary, in a wide temperature range, high changing speed, many times cycling, it will shorten the life time of TECs largely. It’s noteworthy that the absolute life time of TECs depends largely on the total cycling times, not the total time for the cycling.

Different TECs will largely influence failure rate in thermal cycling. TECs with high max. operating temperature have a longer service life than those with low max. operating temperature. This applies to the condition that max. temperature in thermal cycling is far lower than the max. temperature of the TECs. Moreover, there are two factors influencing MTBF in thermal cycling. Small size TEC has fewer thermocouples, which has longer life time than large size one. For large size TEC, heat-mechanical stress is larger and it has more thermocouples, which will increase the possibility of failure under this heat stress. Thus, small size TEC has higher stability than large TECs. There is an actual application. Heat-mechanical stress is produced in TECs. At this time, thermal cycling can be seen as an effective screening technology. Defective TECs can be screened out when TECs are placed in an accurate control cycling. This operation may increase the cost, but it’s necessary when high stability is needed.

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