In this study, the thermal expansion behavior of a cured no-flow underfill material for flip-chip applications was determined by thermomechanical analysis (TMA). The dynamic mechanical behavior of this material was investigated by dynamic mechanical analysis (DMA) at a fixed frequency of 1 Hz. In addition, because the no-flow underfill material is polymer-based and its mechanical properties are influenced by both temperature and time, it is important to consider its viscoelastic behavior. This was accomplished by conducting time-temperature superposition (TTS) experiments using DMA. From the results, master curves have been constructed for both the storage and the loss moduli as a function of frequency at a pre-selected reference temperature. Shift factors were also determined as a function of temperature, and they can be fitted using the Williams-Landel-Ferry (WLF) equation. Based on the master curves, one can obtain the relaxation modulus, E(t,T), as a function of time and temperature. The measured thermomechanical and viscoelastic properties of the no-flow underfill material provided crucial material properties for accurately modeling the package stress.
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