Implementation of moisture diffusion model in multi-material system including air cavities

Polymeric materials are often used in assembling and packaging MEMS devices. Polymers are prone to absorb moisture which can lead to reliability issues and different types of failures of the package. In contrast to the IC components cavities are usually essential part of the MEMS devices. The gas tightness of these cavities must be ensured for proper operation. This paper presents an extension of the moisture diffusion simulation methodology towards gas filled cavities embedded in multi material systems. The formulation involves the transformation of convection diffusion vapour transport equation into the form of a general transport equation which is solved by a commercially available simulation package. The implementation allows the coupling of additional physical models to the simulation such as condensation models.