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Experimental Characterization and Viscoplastic Modeling of the Temperature Dependent Material Behavior of Underfill Encapsulants

[+] Author Affiliations
Nusrat J. Chhanda, Jeffrey C. Suhling, Pradeep Lall

Auburn University, Auburn, AL

Paper No. IPACK2011-52209, pp. 749-761; 13 pages
  • ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems
  • ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2
  • Portland, Oregon, USA, July 6–8, 2011
  • ISBN: 978-0-7918-4462-5
  • Copyright © 2011 by ASME


In this work, the viscoplastic mechanical response of a typical underfill encapsulant has been characterized via rate dependent stress-strain testing over a wide temperature range, and creep testing for a large range of applied stress levels and temperatures. A specimen preparation procedure has been developed to manufacture 80 × 5 mm uniaxial tension test samples with a specified thickness of .5 mm. The test specimens are dispensed and cured with production equipment using the same conditions as those used in actual flip chip assembly, and no release agent is required to extract them from the mold. Using the manufactured test specimens, a microscale tension-torsion testing machine has been used to evaluate stress-strain and creep behavior of the underfill material as a function of temperature. Stress-strain curves have been measured at 5 temperatures (25, 50, 75, 100 and 125 C), and strain rates spanning over 5 orders of magnitude. In addition, creep curves have been evaluated for the same 5 temperatures and several stress levels. With the obtained mechanical property data, several viscoelastic and viscoplastic material models have been fit to the data, and optimum constitutive models for subsequent use in finite element simulations have been determined.

Copyright © 2011 by ASME



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