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Electromigration of eutectic SnPb flip chip solder joints and their mean-time-to-failure (MTTF) have been studied in the temperature range of 100 to 140 °C with current densities of 1.9 to 2.75×10[sup 4] A/cm[sup 2]. In these joints, the under-bump-metallization (UBM) on the chip side is a multilayer thin film of Al/Ni(V)/Cu, and the metallic bond-pad on the substrate side is a very thick, electroless Ni layer covered with 30 nm of Au. When stressed at the higher current densities, the MTTF was found to decrease much faster than what is expected from the published Black’s equation. The failure occurred by interfacial void propagation at the cathode side, and it is due to current crowding near the contact interface between the solder bump and the thin-film UBM. The current crowding is confirmed by a simulation of current distribution in the solder joint. Besides the interfacial void formation, the intermetallic compounds formed on the UBM as well as the Ni(V) film in the UBM have been found to dissolve completely into the solder bump during electromigration. Therefore, the electromigation failure is a combination of the interfacial void formation and the loss of UBM. Similar findings in eutectic SnAgCu flip chip solder joints have also been obtained and compared. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the measurement of shear strengths of the solder joints for Sn-Ag eutectic alloy with the Au/electroless Ni(P)/Cu bond pad for three different electroless Ni(P) layers. Investigation of fracture surfaces by scanning electron microscopy equipped with energy dispersed x-ray; Increase in shear strength when the P-rich Ni layer disappears from a prolonged reaction.

The effect of stress on the microstructural characteristics and grain growth and void formation in submicrometer aluminum thin films were investigated. The results showed that grains grew during Al deposition. However, voids were only observed in the confined samples. In the confined samples, stepwise annealing at 400 degrees celsius caused retarded grain growth. As for unconfined samples, abnormal grain growth was observed at only 200 degrees celsius.

The whisker growth caused by the ntermetallic compound formation in Sn-0.7Cu flip chip solder joints under electromigration is analyzed. The amount of the intermetallic compound is shown to be main determinant factor of the difference of mass extrusion.

Polychromatic microfocused synchrotron x-ray beam is used for measuring the bending and residual stress of flip chips caused by the mismatch of thermal expansion between the chip and the substrate. The studies have shown that thermal stress on the circuits and the solder joints in a flip chip has depended on temperature and the distance from the center of the chip, which has shown that interconnects at the corner and edge of a flip chip are of reliability concerns.

In situ synchrotron x-ray white beam microdiffraction is used for studying the electromigration-induced hydrostatic elastic stress in Pb-free SnCu solder joints. The compressive stress gradient between the cathode and the anode is much larger than that is required for initiating Sn whisker growth and the effective charge number of [beta]-Sn derived from the electromigration data has agreed well with the calculated value.

In situ stress measurements were performed during high frequency pulse electrodeposition of nanotwinned Cu thin films to understand the periodic stress changes during pulse-on and pulse-off periods. The stress profile showed an abrupt increase in tensile stress to about 400 MPa during the pulse-on period and a stress relaxation during the pulse-off period.

The thermal stability of {111}/ nanotwins is studied by in situ transmission electron microscopy (TEM) characterization. The studies have shown that inverse migration of (112) twin boundary driven by a high strain is possible if sufficient stress is applied to the copper.

An in-depth synchrotron radiation based white beam x-ray microdiffraction study of plasticity in individual grains of an Al (Cu) interconnect during the early stage of electromigration (EM) is described. The analysis has shown a rearrangement of the geometrically necessary dislocations (GNDs) in bamboo typed grains during that stage.

Composite SnPb flip chip solder joints are used to study the combined effect of electromigration and thermomigration. The result has shown that at the last stage of void propagation, due to large Joule heating and bad heat dissipation, the composite solder joint partially melted before an electrical opening occurred.

The composite solder joints of 97Pb-3Sn and 37Pb-63Sn are examined at room temperature under high current densities to investigate the effect of current density and Joule heating on electromigration-induced failure. Simulation is used to show the effect of voids formed during electromigration tests by emphasizing the effect of current crowding and Joule heating on electromigration-induced failure.

The role of 0.5 wt % Cu in the base Sn-3.5%Ag solder is highlighted to reduce the dissolution of the Cu bond pad in ball grid array applications. It was found that after 0.5 wt% Cu addition, the rate of dissolution of Cu in the molten Sn-3.5%Ag solder slowed down significantly.

Mechanical strengths of the solder joints for Sn-Ag eutectic alloy with the Au/electroless Ni(P)/Cu bond pad were measured for three different Ni (P) layers. Results reveal that the formation of crystalline phosphorous-rich Ni layer at the solder interface of Au/electroless Ni (P)/Cu bond pad with Sn-Ag eutectic alloy deteriorates the mechanical strength of the joints severely.

The electromigration damage in flip chip solder bumps of eutectic SnPb and SnAg(sub 3.8)Cu(sub 0.7) was studied after current stressing at 120 degrees C. with 1.5 A. For eutectic SnPb, the effective charge number, Z*, is about 36-100 after 39.5 h of electromigration, but for SnAg(sub 3.8)Cu(sub 0.7) the marker movement was too small to measure Z* even after 200 h of current stressing.