Eutectic solder lines were prepared, for electromigration studies, by means of re-flow into V-shaped grooves which were etched into (001) Si wafer surfaces. The thick lines were highly reproducible. Lines which were 100µm-wide and 150 to 800µm long were stressed with a current density of 2.8 x 104A/cm2 at 150C. The accumulation of large lumps of the alloy, rather than hillocks of Sn or Pb, was observed at the anode. Depletion and voiding were observed at the cathode. Measurements of the volume of the lump indicated that the average effective charge number for electromigration in the eutectic was 33. This was close to the reported value of 47 for self-electromigration in bulk Pb. The use of X-ray dispersion analysis showed that Pb was the predominant diffusing species.

Electromigration in Eutectic SnPb Solder Lines. Q.T.Huynh, C.Y.Liu, C.Chen, K.N.Tu: Journal of Applied Physics, 2001, 89[8], 4332-5