Abstract
Microstructural changes induced by electromigration were studied in eutectic SnAg solder bumps jointed to under-bump metallization (UBM) of Ti/Cr-Cu/Cu and pad metallization of Cu/Ni/Au. Intermetallic compounds (IMCs) and phase transformations were observed during a current stress of 1 × 104 A/cm2 at 150 °C. On the cathode/substrate side, some of the (CuyNi1−y)6Sn5 transformed into (NixCu1−x)3Sn4 due to depletion of Cu atoms caused by the electron flow. It is found that both the cathode/chip and anode/chip ends could be failure sites. On the cathode/chip side, the UBM dissolved after current stressing for 22 h, and failure may occur due to depletion of solder. On the anode/chip side, a large amount of (CuyNi1−y)6Sn5 or (NixCu1−x)3Sn4 IMCs grew at the low-current-density area due to the migration of Ni and Cu atoms from the substrate side, which may be responsible for the electromigration failure at this end.
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Chen, Y.H., Shao, T.L., Liu, P.C. et al. Microstructural Evolution During Electromigration in Eutectic SnAg Solder Bumps. Journal of Materials Research 20, 2432–2442 (2005). https://doi.org/10.1557/jmr.2005.0291
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DOI: https://doi.org/10.1557/jmr.2005.0291