High temperature aging of epoxy-based molding compound and its effect on mechanical behavior of molded electronic package

Abstract

Epoxy-based molding compounds (EMC) are widely used to encapsulate automotive electronics. Under high temperature operation, EMC is oxidized and undergoes degradation in mechanical properties. This can alter the thermomechanical behavior of encapsulated electronic components, and thus can affect their reliability. Three key aspects of EMC oxidation in the context of microelectronics reliability are presented in this paper – (1) degradation of EMC specimens is studied under high temperature aging at three different temperatures – 170°C, 200°C, and 230°C for up to 1500 hours and the oxidation growth is documented as a function of aging duration and temperature using a fluorescence microscope; (2) critical thermomechanical properties of oxidized EMC (viz., elastic modulus, thermal expansion coefficient, and glass transition temperature) are experimentally characterized using fully-oxidized specimens; (3) the effect of EMC oxidation on thermomechanical behavior of an electronic package is investigated by comparing the deformation of a thermally aged package with that of a pristine package under a thermal cycle. This study indicates that EMC oxidizes rapidly during early stages (≈ 24 hours) of exposure to high temperature, and the oxidized layer exhibits significantly different thermomechanical properties. Thus, thermal aging develops a much stiffer package behavior, which is crucial for an accurate reliability assessment.