The Constitutive Creep Equation for a Eutectic Sn-Ag Alloy Using the Modified Theta-Projection Concept

Yoshiharu Kariya, Masahisa Otsuka, William J. Plumbridge

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26 Citations (Scopus)


Creep data for a eutectic tin-silver alloy at temperatures between 298 K and 398 K have been analyzed using the modified theta-projection concept, instead of the steady-state creep constitutive equation in the following formula: εcr = A (1 - exp(-αt)} + B (exp(αt) - 1}, where A, B, and a are constants to be experimentally determined. The equation describes well the creep curves of the eutectic tin-silver alloy up to the tertiary stage. All constants exhibited power law relationships with the applied stress. The rate constant, α, has a high stress exponent, which is attributed to dispersion strengthening. The rate constant a and the strain factor B only showed temperature dependence, while the strain factor A was independent of temperature. The activation energy for α was 65 kJ/mol at high stresses and 90 kJ/mol at low stresses. The energies suggest that the dislocation pipe diffusion and the lattice diffusion are predominant at high stresses and low stresses, respectively.

Original languageEnglish
Pages (from-to)1398-1402
Number of pages5
JournalJournal of Electronic Materials
Issue number12
Publication statusPublished - 2003 Dec
Externally publishedYes



  • θ projection
  • Constitutive equation
  • Creep
  • Lead-free solder
  • Nonsteady state
  • Sn-3.5Ag

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials
  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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