Accelerated life tests criticism

Differences of opinion have existed for decades with respect to the mixture of corrosive gases that should be used in test chambers. For air-conditioned electronic equipment rooms in urban environments that are well removed from industrial pollution (Class II Battelle environment, G1 IBM environment, and lEC Class II environment), the appropriate Battelle accelerated life test calls for use of 200 ppb NO2, 10 ppb H2S, and 10 ppb CI2 at an RH of 70 %. This test does an excellent job of simulating corrosion films on silver, copper, tin, and some gold-plated metals, but has been criticized in recent years because the Aims it produces on nickel are unrealistic. 

ASLT (accelerated shelf life testing) must also be run on the sensor and its individual components to define realistic shelf life, storage conditions, and usage conditions. This information is also critical to the overall quality control for the sensor and the instructions for its use. 

Accelerated testing depends critically on selecting a parameter whose effect on service life is so well understood that long lifetimes at low values of the parameter can be predicted from shorter lifetimes at higher values. The parameter may be the prime cause of degradation, such as in a stress-rupture test where longer lifetimes at lower loads are predicted by extrapolation from short lifetimes at higher loads. It can also be a secondary parameter, such as when temperature is increased to accelerate chemical attack while the principal factor, chemical concentration, is kept constant. This is because there is more confidence in the relation between rate of reaction and temperature than in the relation of rate of reaction to concentration. It is clearly essential that extrapolation rules from the test conditions to those of service are known and have been verified, such that they can be used with confidence. 

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