Electromigration in tin-bismuth planar solder joints

A novel planar solder geometry is described that allowed real-time. non-destructive monitoring of the rate of bismuth segregation at the anode in eutectic Sn-Bi solder joints of lengths in the range 180-450 µm at various current densities and temperatures while tracking the extent of electromigration by electrical resistance means. The rate of bismuth segregation was found to be somewhat proportional to the solder joint length indicating a probable Blech back-stress effect. Initially, the solder joint electrical resistance decreased followed by an increase. The period of decreasing electrical resistance was much less at higher current densities. The electromigration activation energy was determined to be 0.92 eV.