Advanced moisture diffusion modeling and characterisation for electronic packaging

Thermal-moisture analogy based on "wetness" technique has earlier been developed that enables modeling of moisture diffusion in the electronic packages during moisture preconditioning using commercial FEA software. In this paper, this "wetness" technique has been extended to model moisture diffusion in a multi-material package under a dynamic boundary condition such as experienced by the package during solder reflow, autoclave or temperature-humidity cyclic tests. The implementation procedures using commercial FEA software are described in detail. Significant developments have also been made in the characterisation of moisture sorption and diffusion properties of the packaging materials. This includes non-Fickian sorption, anisotropic diffusion, as well as high temperature diffusivity. A formula was also proposed to account for the effect of in-plane diffusion for a specimen with low aspect ratio.