Creep behavior of eutectic Sn-Cu lead-free solder alloy

Tensile creep behavior of precipitation-strengthened, tin-based eutectic Sn-0.7Cu alloy was investigated at three temperatures ranging from 303-393 K. The steady-state creep rates cover six orders of magnitude (10(-3) - 10(-8) s(-1)) under the stress range of sigma/E = 10(-4) - 10(-3). The initial microstructure reveals that the intermetallic compound Cu6Sn5 is finely dispersed in the matrix of beta-Sn. By incorporating a threshold stress, sigma(th), into the analysis, the creep data of eutectic Sn-Cu at all temperatures can be fitted by a single straight line with a slope of 7 after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation-pipe diffusion in the tin matrix. So the steady-state creep rate, (epsilon) over dot, can be expressed as (epsilon) over dot = AGb/RT(sigmath/G)(7) exp(-Q(C)/RT), where Q(C) is the activation energy for creep, is the temperature-dependent shear modulus, b is the Burgers vector, R is the universal gas constant, T is the temperature, sigma is the applied stress, A is a material-dependent constant, and sigma(th) = sigma(OB)root1 - k(2)(R), in which sigma(OB) is the Orowan bowing stress, and k(R) is the relaxation factor.