Characterization of Linear Viscoelastic Behavior of Epoxy Molding Compound Subjected to Uniaxial Compression and Hydrostatic Pressure

The linear viscoelastic properties of epoxy molding compound (EMC) are measured by an embedded fiber Bragg grating (FBG) sensor. A single cylindrical EMC specimen is fabricated, and it is subjected to constant uniaxial compression and hydrostatic pressure at various temperatures. The FBG embedded in the specimen records strain histories as a function of time. Two linear viscoelastic properties (Young's modulus and bulk modulus) are determined from the strain histories. The master curves of two properties are produced, and the corresponding shift factors are determined using a piecewise function. The validity of three major assumptions associated with the linear viscoelasticity-thermorheological simplicity, Boltzmann superposition, and linearity-is verified by supplementary experiments. The accuracy of the measured properties is corroborated by the warpage measurement of a bimaterial specimen subjected to a temperature cycle. The effect of the time-dependent bulk modulus on the warpage is also discussed.