COMPARISON OF CREEP LIFE ASSESSMENT BETWEEN TIN-BASED LEAD-FREE SOLDERS AND LEAD SOLDERS

The creep properties of tin-based lead-free solders Sn3.0Ag0.5Cu and Sn0.7Cu0.1Ni and lead solders 10Sn90Pb and 50Sn50Pb were investigated at temperatures between 298 K and 398 K. The creep-rupture time decreases with increasing initial stress and temperature. The analysis of the solder creep curves uses the Omega method. The creep rate (epsilon) over dot is expressed by following formula: In (epsilon) over dot = In (epsilon) over dot(0) + Omega epsilon, where (epsilon) over dot(0) and Omega are experimentally determined. The parameter (epsilon) over dot(0) increases with increasing initial stress and temperature. The activation energy for (epsilon) over dot(0) is 108 kJ/mol for Sn3.0Ag0.5Cu and 85 kJ/mol for Sn0.7Cu0.1Ni. These energies suggest that the lattice diffusion of tin is dominant. The energy of 10Sn90Pb is 37 kJ/mol and that of 50Sn50Pb is 67 kJ/mol. The creep-rupture time is calculated using the parameters, (epsilon) over dot(0) and Omega. The calculated creep-rupture time is in good agreement with the measured creep-rupture time.