Dynamic mechanical analysis such as tension test allows for studying the fatigue failure of polymer materials. By increasing the dynamic strain or stress amplitude, the fatigue and failure of material could be characterized. Silica-filled epoxy molding compounds are widely used in modern electronic industry, to protect the silicon chip from mechanical, chemical and thermal effects. There is insufficient information on fatigure reliability of plastic encapsulated electronic components capable of surviving high temperatures for long periods (>100,000 hours). In this paper, the details of the procedure for fatigue effect measurement are described. Feddersen’s approach for fracture toughness test method is applied. Low cycle fatigue is investigated for pristine samples. The aging effects of a number of epoxy molding compounds subjected to sustained high-temperature long-term aging have been studied. Two popular molding compounds, EMC-1 and EMC-2, are studied under three aging temperatures: 100C, below the glass transition temperature, and 150 °C, above the glass transition temperature, from pristine to 120 days aging. The crack propagation under constant or increasing stress or strain has been recorded and discussed.