Characterization and Verification of Viscoelastic Constitutive Parameters of Underfill Material

The continuous miniaturization and intelligentization of electronic products have promoted the development of microelectronic packaging technology. Underfill is one kind of widely used polymer materials in microelectronic packaging, which shows an obvious viscoelastic behavior, i.e., the modulus highly depends on both temperature and time. In many circumstances, the viscoelastic behaviors are often not characterized to reduce the experimental and computational cost. However, accurately characterizing the viscoelastic behavior of the underfill can further obtain a more credible simulation result. In this paper, frequency dependent dynamic mechanical analysis (DMA) measurements are performed on a self-developed underfill by the double cantilever to characterize its viscoelastic behaviors. Through the assumption of time temperature equivalence (TTE), we can obtain the master curve by shifting the experimental data. Meanwhile, shift factors are carried out by shifting the experimental data using the TTE and Prony pairs parameters based on the generalized Maxwell model are obtained by fitting the master curve. Finally, uniaxial tension is performed to verify the accuracy of viscoelastic material parameters. The simulation results using viscoelastic parameters show good correlation to experimental results, which proves that the developed viscoelastic models could successfully predict the rate-dependent non-linear stress-strain behavior, and might be used to generate more accurate stress behavior in package structure.