Experimental study and constitutive analysis of compressive creep behavior of solder material in IGBT modules

The compressive creep behavior of eutectic tin-lead (Sn-Pb) alloy was studied through constant-load creep experiments on bulk specimens. These specimens were exposed to constant compressive stresses ranging from 10% to 100% of their yield strength, at temperatures escalating from room temperature (RT) to 140°C. Constitutive analysis of the primary creep rate revealed the inadequacy of a single power-law stress function. In the high-stress regime across these temperatures, a hyperbolic sine function effectively correlated the transient creep rate with the applied stress. Conversely, in the low-stress regime, a linear function aptly approximated the stress dependence of the transient creep rate. Modifications were made to the classical Norton-Bailey time/strain hardening model to accurately represent the unique primary creep characteristics of this alloy. Given the distinct stress functions of the transient creep rate, dislocation creep and diffusion creep were identified as the predominant creep mechanisms in the high and low-stress regimes, respectively. This comprehensive experimental investigation and constitutive analysis facilitated the construction of a transient creep deformation map, illuminating the underlying creep mechanisms of eutectic Sn-Pb alloy under varying stresses at elevated temperatures.