After 25 years in the reliability field I am still a bit mystified by the humidity testing. Generally the environmental tests can be divided into two major categories: Durability tests, where some form of wear-out mechanism causes products to fail. The most common examples of durability tests are vibration and thermal cycling. The second group is the capability tests, often referred as overstress tests with the goal of determining how well the product can resist certain conditions such as high voltage, accidental drop, dust, or others. It appears that humidity tests belong somewhere in between the two categories. On one hand there are electro-migration, corrosion, dendritic growth, and other failure mechanisms following the pattern of wear-out processes. Those failure mechanisms are …
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