Structural Analysis on Interfacial Failure among Dissimilar Materials Caused by Thermal Stress

Abstract

In order to raise the reliability of advanced industrial products such as integrated circuit substrates, the interfacial failures among dissimilar materials caused by the mismatch of their mechanical and/or thermal properties are investigated. The purpose of the present study is the structural analysis on interfacial failures and materials design that prevent these failures. The results on the interfacial failures in the Si-epoxy system during the temperature-cycling loading of 200 to 150 °C show that the crack is initiated at the Si-epoxy interface in the first cycle, and its growth rate decreases with increasing cycle number. However, the initiation point of the crack is not the corner of the silicon chip, where thermal stress is expected to be concentrating. Based on the obtained results, the mechanism of the interfacial failures was discussed. As an approach for the second purpose, the reduction of thermal stress at the interface has been proposed in this study through the controlling of the materials' morphology. It was suggested from the experiments or the computer simulations that the thermal stress at the metal-polymer interface can be reduced by controlling the thermal expansion of polymer by applying organic/(nano-porous inorganic) composites or by applying a porous metal whose Young's modulus is much lower than that of a non-porous metal to the composite.