Time-dependent Fracture Mechanics Approach to Crack Growth of Solder

Abstract

Time-dependent fracture mechanics parameter (C*) has been used to characterize the crack growth behavior of Sn-Pb eutectic solder (63Sn-37Pb) from crack growth (CG) tests under cyclic loading with various hold times (5, 20, 30, 50, 100 seconds), low cycle fatigue (LCF) tests under various frequencies (10 -3 -10 -1 Hz), and creep crack growth (CCG) test. The results showed that CG, LCF, and CCG processes of Sn-Pb eutectic solder were dominated by time-dependent mechanism, and C*-parameter could be successfully correlated with their crack growth rates, i.e. the plots of C* -da/dt located within a scatter band with an exponent of 1. Although crack growth behavior was essentially time-dependent, crack growth mechanism was varied between under short hold time and long hold time. SEM observations of the longitudinal sections of CG specimens revealed that cracks under short hold time conditions propagated in transgranular manner through the Sn-Pb colonies, while those under long hold time conditions propagated in intergranular manner around the Sn-Pb colony boundaries.