Abstract
This paper discusses electro-migration behavior of eutectic Sn-Bi solder with Cu-pillar bumps. Two types of under bump metal (UBM) of organic substrate were studied, that is, Cu pad and electroless Ni/Au plated on Cu pad. The current density was 4x104A/cm2 at 125 and 150 degree C. Bi quickly migrated to accumulate on the anode side(Cu-pillar) and Sn migrated to the cathode side (Substrate pad). Both the case of surface finishes, although the resistivity was increased to approximately 80 % during approximately 80 hours, it was stabilized more than 2800 hours and there were no electrically break failure. From the cross-sectional analyses of eutectic Sn- Bi solder joints after the test, it was found that Bi layer and intermetallic compound (IMC) behaved as the barriers of the Cu atom migration into Sn solder.
