This study investigates moisture diffusion characteristics of electronic packaging materials exhibiting Fickian and nonFickian behavior. Experimental investigation involves moisture absorption and desorption tests of homogenous underfill materials and inhomogeneous organic substrates as examples of Fickian and non-Fickian solids, respectively. In absorption tests, samples are dried out in an oven prior to testing in a humid environmental chamber. In desorption tests, samples are saturated in the environmental chamber under a specified temperature and relative humidity prior to the moisture desorption inside the oven. Samples in both tests are taken out of the test environments and weighed frequently to obtain moisture weight change data. Using the measurements from testing several different Fickian and non-Fickian materials, diffusivity/moisture concentration relationships are constructed. These relationships are implemented into a customized finite element simulation tool under the ANSYS® platform. Finally, the experimental tests on multi-material specimens are simulated by using this tool in order to establish its validity.