Measurement and Characterization of the Moisture-Induced Properties of ACF Package

Abstract

This study is to observe the exact behavior of anisotropic conductive adhesion (ACF) package under humid environments by obtaining the moisture-induced properties such as diffusion coefficient (the rate of moisture movement into the materials), saturated moisture content (the maximum absorbed quantity), and swelling coefficient (length change due to the chemical interaction). So the experiments were performed to get the moisture-induced properties of ACF and FR4 using newly developed method at various temperature and relative humidity conditions. Experimental results showed that the diffusion coefficient of ACF and FR4 follows Arrhenius’ equation very well, and the saturated moisture content of them follows Henry’s law, which means linear relationship between saturated moisture content and relative humidity, but the saturated moisture content of ACF is influenced by temperature as well as relative humidity. And the swelling coefficient of ACF and FR4 increases with temperature. Especially in the case of ACF, it shows the dramatic degradation due to Tg (glass transition temperature) at nearby 85°C. Finally, as using these experimental results, the behavior of the ACF package under humid environment is predicted through finite element simulation. When wetness defined by moisture content over saturated moisture content changes from 0 to 0.9, the center of the ACF package is subject to compression and the edge of the ACF package is subject to tension in the case of transient state. After all, because the edge of the ACF package is very weak due to bending moment, the failure is easy to occur under humid environment.