Sukrut Prashant Phansalkar and Bongtae Han
Department of Mechanical Engineering, University of Maryland, College Park, MD, USA
For more information about this article and related research, please contact Prof. Bongtae Han.
Abstract:
The cure-extent dependent viscoelastic behavior of filled thermosets remains a critical issue in high-temperature manufacturing, particularly in advanced semiconductor packaging. This paper presents a novel method for characterizing the evolution of the Young's equilibrium modulus and bulk equilibrium modulus during curing, the properties essential for accurately describing cure-dependent behavior. The method fully resolves the key limitations of existing approaches, namely the unintended additional curing of partially cured specimens during testing, by adopting a distinctively different measurement strategy. First, the autocatalytic cure kinetics and the cure-dependent glass transition temperature are characterized. Partially cured specimens with a relatively low cure extent (p ≈ 0.5) are then fabricated using the cure kinetics model and placed in test chambers preset to the test temperature. he test temperature is chosen to exceed the glass transition temperature sufficiently to achieve complete relaxation. ure extent is tracked in real time through continuous temperature monitoring. Short monotonic tests (≤10 s) are performed to determine the Young's and bulk equilibrium moduli at selected cure extents. The percolation model is extended to describe the evolution of Young's equilibrium modulus by experimentally determining the evolution exponent. For the bulk equilibrium modulus, an additional decay term is introduced to capture its unique behavior, including its high value at the gel point. These enhanced models accurately reproduce the evolution of both equilibrium properties.
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