Coarsening of the Sn-Pb Solder Microstructure in Constitutive Model-Based Predictions of Solder Joint Thermal Mechanical Fatigue

摘要

An expression for the coarsening rate of the Pb-rich phase particles was determined through isothermal aging experiments and comparative literature data as:#lambda# = #lambda#_o + {[4.10 × 10~(-5) e~(-11023/T)+ 15.6 × 10~(-8) e~(-3123/T) (d#gamma#/dt)]t}~0.256where #lambda#_o and #lambda# are the initial and final mean Pb-rich particle diameters, vespectively (mm); T is temperature (degK); t is time (s); and d#gamma#/dt is the strain rate (s~(-1)). The phase coarsening behavior showed good agreement with previous literature data from isothermal aging experiments. The power-law exponent, p, for the Pb-rich phase size coarsening kinetics:#lambda#~p - #lambda#_o~p ≈ tincreased from a value of 3.3 at the low aging temperature regime (70-100deg C) to a value of 5.1 at the hgih temperature regime (135-170deg C), suggesting that the number of short-circuit diffusion paths had increased with further aging. This expression provides an important basis for the microstructurally-based, constitutive equation used int he visco-plastic model for TMF in Sn-Pb solder. The revised visco-plastic model was exercised using a through-hole solder joint configuration. Initial data indicate a satisfactory compatibility between the coarsening expression and the constitutive equation.