Electromigration and critical product in eutectic SnPb solder lines at 100 °C

Due to a significant change in electromigration behavior of eutectic SnPb at different temperatures, it is critical to understand it at the device temperature, i.e., 100 degrees C. In the present study, the electromigration behavior of e-SnPb is investigated at 100 degrees C and at different current densities, varying within the range of 5x10(3)-5x10(4) A/cm(2). The test samples are prepared by reflowing solder into V grooves etched on (001) Si wafers. The electromigration is observed at the current densities higher than 1x10(4) A/cm(2). The dominant diffusing species at 100 degrees C is found to be Pb. The threshold current density for electromigration to occur in e-SnPb comes out to be 5x10(3) A/cm(2). We also notice Pb rich phase coarsening, which becomes significant at high current densities. The results are compared to that in preannealed samples. The effects of the changes in microstructure on the electrical reliability are also discussed. The interface diffusion is dominant when the grain size is small. Subsequently, as the grain size increases, it is reduced to the order of the lattice diffusion, and therefore the electromigration is impeded. The critical product for e-SnPb solder is estimated to be 150 experimentally, and is also compared to the theoretically calculated value of 8. The reason for the discrepancy is discussed. (c) 2006 American Institute of Physics.