Moisture absorption and desorption in epoxy mould compounds: Characterization of Fickian and non-Fickian behaviours in complex packages

Abstract

This works analyses the moisture absorption and desorption in three different mould compounds used in QFN packaging technology. Moisture diffusion during accelerated tests is replicated on different sample type: bulk material, empty QFN strips and empty QFNs to examine the diffusion modes. The temperature-dependent diffusion parameters are characterised using the Dual stage model. The combination of a Fickian and a non-Fickian behaviour of this model fits perfectly the diffusion results in a bulk resin sample. However, the diffusion parameters in the case of the QFN strips and packages suggest a non-negligible diffusion along the interfaces. The desorption analyses in these QFN samples show residual moisture. We suspect the presence of residual moisture at the leadframe/moulding interfaces. The desorption at standard industrial temperatures highlights anomalies, suggesting a critical thermal aging phenomenon.