Electromigration damage in solder bumps of eutectic Sn-Pb, and SnAg3.8Cu0.7, was studied after current stressing using 1.5A at 120C. The diameters of the bumps were of the order of 200µm. The under-bump metallization on one side was electroless Ni, and on the other side was electroplated Cu. Surface marker motion was used to measure atomic fluxes and calculate effective charge numbers. In the case of eutectic Sn-Pb, the effective charge number was between 36 and 100; after 39.5h of electromigration. In the case of SnAg3.8Cu0.7, the marker movement was too small to measure; even after 200h of current stressing. Although the effect of electromigration in SnAg3.8Cu0.7 was much smaller than in Sn-Pb, hillocks of intermetallic compound at the anode were observed in the former case.

Electromigration of Eutectic SnPb and SnAg3.8Cu0.7 Flip Chip Solder Bumps and Under-Bump Metallization. T.Y.Lee, K.N.Tu, D.R.Frear: Journal of Applied Physics, 2001, 90[9], 4502-8