Temperature and humidity effects on moisture diffusion in epoxy molding compound based on Fickian, dual-stage and Langmuir models

Epoxy molding compound (EMC) is a critical material in advanced packaging, as its moisture diffusion behavior significantly impacts the long-term reliability of packaged devices. The moisture diffusion behavior of EMC was investigated under varying temperature and humidity conditions through moisture absorption experiments, and the corresponding diffusion mechanisms were analyzed using the Fickian, dual-stage, and Langmuir models. The results showed that the Fickian model was only applicable under low humidity and temperature conditions. Although the dual-stage model fitted well, its assumption of “independent diffusion of bound water” contradicted experimental observations. The Langmuir model also achieved high fitting accuracy. This study also established temperature–humidity-dependent functions for EMC moisture-related parameters. As the temperature increased, the bound water content increased exponentially, along with the transformation probability of free-bound water and the diffusion coefficient. Under medium humidity, the moisture content increased linearly with humidity, while the transformation probability and diffusion coefficient decreased linearly. At high humidity, capillary condensation became the dominant process, leading to a sharp increase in saturated moisture content, diffusion coefficient, and conversion probability. Low-temperature liquid-nitrogen adsorption experiments confirmed the occurrence of capillary condensation. • Studied moisture uptake actions in epoxy molding compound from 40–80 C and 40%–85% humidity. • Langmuir diffusion model gave clearer physics mechanism and accuracy close to dual-stage. • Moisture parameters follow linear humidity and Arrhenius temperature laws. • Capillary condensation above 75% RH confirmed by nitrogen adsorption isotherms.