Low temperature electromigration and thermomigration in lead-free solder joints

High current density and high temperature gradient are major reliability concern for next generation high density power electronics. High current density experiments on lead free solder joints coated with NiAu and non-coated Cu pads were conducted at -20°C, -30°C, -40°C and -50°C ambient temperatures. The time to failure (TTF) shows that solder joints with NiAu coated Cu pads last longer. Results also indicates TTF plot shows that TTF rate increases exponentially when the solder joint temperature is higher than 64% of its melting temperature, and decreases exponentially reaching the maximum lifetime when the temperature is below this threshold temperature. The mass transport activation energy, E_a was determined using the test data and it was found to be 2.67 ± 0.05 and 3.65 ± 0.13 eV for coated and non-coated solder joints, respectively. These values are indicative of the dominant diffusion mechanism during the experiment. It was discovered that the thermomigration driving force was as high as electromigration driving force.