Epoxy molding compound (EMC) is widely used for encapsulating automotive electronics. Among all of the components of an electronic package, EMC is most exposed to the atmosphere, and thus undergoes aging. During high-temperature operation, EMC is oxidized, which alters its mechanical properties, and thus can affect the reliability of electronic components. This chapter focuses on four key aspects of EMC oxidation – (1) the growth of EMC oxidation layer, (2) the mechanical properties of oxidized EMC, (3) the effect of oxidized EMC on thermomechanical behavior of a molded package, and (4) the effect of EMC oxidation on solder joint reliability. This study utilizes various experimental characterization techniques as well as finite element simulation-based analysis.