Thermal stress in semiconductor encapsulating materials

To examine molding-compound-induced stresses, and to determine the influence of the time-dependent and temperature-dependent thermomechanical properties of the molding compound, a linear viscoelastic analysis has been applied to a simple bilayer structure. Stress generation is examined over the temperature range from -150 degrees C to the molding temperature (180 degrees C), based on a complete consideration of the thermomechanical properties of a molding compound. Stress calculations are compared to experimentally determined radii of curvature of the bilayer structure as a function of temperature. Both calculated and experimental results demonstrate the necessity to consider a complete materials description in order to adequately describe stress generation. The importance of the viscoelastic contribution of the transition range and the temperature-dependent elastic contribution of the glassy state to stress generation are highlighted.<
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