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

Authors: Kariya, Yoshiharu; Otsuka, Masahisa; Plumbridge, William J.

Source: Journal of Electronic Materials, Volume 32, Number 12, 1 December 2003 , pp. 1398-1402(5)

Publisher: Springer

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Abstract:

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: ε_cr = A {1 - exp(-αt)} + B {exp(αt) - 1}, where A, B, and 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.

Keywords: CREEP; NONSTEADY STATE; SN-3 5AG; LEAD-FREE SOLDER; CONSTITUTIVE; EQUATION; PROJECTION

Document Type: Research article

Publication date: 2003-12-01