Modeling moisture caused failures in stress tests

The most important time related parameter of electronic systems is MTTF (mean time to failure). In accelerated aging tests, the circuits are exposed to enormously harsh environmental conditions. The accelerating parameters and events like mechanical vibration and shock, temperature, pressure, humidity and their combinations are used as loads in stress test methods. There are different models to describe the effects caused by the mentioned stresses. In most cases, these models only include some of the parameters, but none describe all the possible effects of a stress test. By obtaining more information about the materials used in the test vehicle and integrating the available models, it is possible to derive a mostly complete model of moisture permeation, including ad-/absorption and diffusion effects. This paper gives an overview of the available models and shows a first-enclosing simulation of moisture penetration.