The thermal-mechanical properties of the materials currently used in packaging are being reexamined as the electronic packaging industry moves towards chip scale packages and wafer scale packages. The rate-dependent transition of elastic modulus and viscosity from thermal softening to thermal hardening with rising temperature, which does not involve any phase change, has been observed in certain elastomers. An explanation about this interesting phenomenon is given based on thermodynamic considerations. A theoretical analysis is performed to show the limitation of existing viscoelastic models in predicting the transition. It appears that macroscopic material properties should be reexamined based on the physics behind the interaction between ordinary elasticity and entropic elasticity.
Rate-Dependent Transition From Thermal Softening to Hardening in Elastomers
Contributed by the Applied Mechanics Division of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS for publication in the ASME JOURNAL OF APPLIED MECHANICS. Manuscript received by the ASME Applied Mechanics Division, April 23, 2002; final revision, November 10, 2002. Associate Editor: M.-J. Pindera.
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Chen, Z., Atwood , J. L., and Mai , Y. (August 25, 2003). "Rate-Dependent Transition From Thermal Softening to Hardening in Elastomers ." ASME. J. Appl. Mech. July 2003; 70(4): 611–612. https://doi.org/10.1115/1.1571860
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