Geometry Effects on the Electromigration of Eutectic SN/PB Flip-Chip Solder Bumps

Abstract

This work investigates the effect of passivation opening diameter and underbump metallization (UBM) diameter on the electromigration (EM) resistance of Sn/Pb eutectic solder bumps. For the bump geometries studied, the electromigration lifetime depends strongly on the UBM area but weakly on the passivation opening area. The applicability of Black's model for extrapolating lifetime from accelerated currents to operating currents is investigated. The thermal activation energy, E A , is approximately 1.0 eV and the current density exponent, n, is approximately 2.0. While Black's model for current density acceleration appears to apply, the current density exponent may not be transferable between bumps of different geometries. A physical model of voiding within the bump using finite element analysis is proposed to explain the observed results.

Effects of Current Stressing and Isothermal Aging on the Tensile Strength of Microscale Lead-Free Solder Joints with Different Joint Volumes

“…For these solder joints without current stressing test, the fracture mode turns to be ductile fracture and the fracture position locates in the mid of the solder, while for these solder joints after 48h current stressing test under 1.0×10 4 A/cm 2 current density rupture at the cathode IMC/solder interface regardless of their joint height, mainly due to the polarity effect and voids formation, thus causes mixed fracture modes (both ductile and brittle fracture). In addition, some recent literatures reported that thermogration may create a synergistic effect on electromigration [10][11][12].The temperature gradient is different when the diameter of the solder joints is same while the height is different, so the effect of thermomigration is also different. Under same direct current density and loading time, the larger joint height is, the greater the temperature gradient is in the solder joints, therefore, thermomigration accelerated the effect of electromigration on the degradation of the tensile strength of solder joints.…”