THEORY OF ENDOCHRONIC CYCLIC VISCOPLASTICITY OF EUTECTIC TIN/LEAD SOLDER ALLOY

摘要

In this paper, a theory of Endochronic cyclic viscoplasticity of eutectic Tin/Lead (60Sn/40Pb) solder alloy under cyclically thermomechanical strain histories had been established. Under the conditions of isotropic and inelastically incompressible small deformation, the constitutive equation of deviatoric behavior was expressed as: S=2∫_0~Z(ρ_0e~(-K(Z-Z'))) /((Z-Z')~α) (partial deriv e~(IN))/(partial deriv Z') dZ' here de~(IN) ≡ dε- dS/2μ and the strain rate dependent intrinsic time scale dZ = dξ / f (ξ, T), dξ, = k || de~(IN)|| / h_0 (ξ , T) and ξ = ξ/ξ_0 Employing the experimental cyclic shear stress-strain curves of various testing temperature and frequency, all temp. dependent material parameters ρ_0, K, α and f(ξ, T). / k =f_0 (T) ; and the temp.-freq. dependent material function h_0(ξ , T) were determined for temp. between 213K and 423K and freq. between 0.3Hz and 0.0lHz. Predicative capability of the theory were then challenged by a set of experiments with complicate strain history such as (ⅰ) Fast in tension/Slow in compression constant strain amplitude cyclic tests (ⅱ) Slow-Fast-Slow constant amplitude cyclic tests. Through the excellent computational results, the present theory demonstrated that it can, not only play a vital role in the area of electronic solder mechanics, but also meet the needs of reliability analysis and life assessment in the electronic/photoelectronic packagings.