Non-Fickian moisture uptake characterisation of epoxy-based moulding compounds with thickness effect

The present work focuses on characterising the moisture uptake behaviour in epoxy-based moulding compounds (EMCs) commonly employed in electronics assembly. Available experimental results on selected EMCs with two different thicknesses of 1.4 mm and 3.0 mm and aged at 60°C/85%RH and 85°C/85%RH are considered. Results showed that at different thicknesses, the initial moisture absorption was similar, and deviated after specific ageing period. This non-Fickian observation indicated thickness-dependent behaviour of the EMCs. In this study, a two-phase moisture uptake model with varying thickness consideration is thus adopted to characterise the moisture uptake in the EMCs. The relationships between the non-Fickian parameters and the thickness are correlated and compared. Results show that the maximum moisture content, M
_m
and non-Fickian initiation time, t
_o
increase, whereas the coefficient of the time delay term, α decreases and the power term, β remains constant with thickness. This enables the prediction of moisture uptake behaviour for various thicknesses of the EMCs that could, in turn reduce the time and cost of extensive experiment works.