Introduction to 85°C/85% relative humidity testing

Accelerated life tests, or tests that stress devices to accelerate fail mechanisms, help evaluate design behaviors during the electronic system development process, as illustrated in Figure 1. Accelerated life testing is important in products or systems that have long life cycles, because studying the behavior for the duration of that lifetime is not usually practical or feasible.

Two such tests – defined by Joint Electron Device Engineering Council (JEDEC) JESD22-A110 and JESD22-A101 standards, respectively – are the biased highly accelerated temperature and humidity stress test (BHAST) and the steady-state temperature humidity bias (THB) life test. These tests are known as 85°C/85% RH tests or 85/85 tests, meaning that the testing exceeds 85°C and 85% RH at the same time.

A BHAST requires 96 hours of electrical biasing while maintaining 130°C and 85% RH, in addition to a vapor pressure of 33.5 PSIA with the goal of accelerating corrosion within the device. In semiconductors, the BHAST test helps ensure that devices will continue operating electrically over extended product life cycles, despite exposure to humid environments, by accelerating the penetration of moisture into the package and die surface.

A THB life test is very similar, with the exclusion of pressure. The stress usually activates the same failure mechanism as a BHAST but with a lower acceleration factor; thus, units are subjected to a longer stress time of 1,000 hours at 85°C and 85% RH.

BHAST and THB tests can be equally useful in system testing. In a chip these accelerated life tests can simulate moisture ingress into a plastic package. In a full system the printed circuit board, connections and other materials can also be affected by humidity in the air over time.[KA1]