Electromigration in tin thin film

Electromigration in flip-chip interconnect is an important reliability issue in modem electronic devices. Tin is a very important element in flip-chip interconnect. In this study, the effect of electromigration on Sri thin film was investigated. We used a new experiment method called TCL (Tin Clad Laminate) to study the electromigration. TCL uses epoxy resin to attach Sn thin film onto FR5 substrate. Afterwards, the three-layer structure was passed through a thermal press to securely bond them together. The Sri film thickness is about 30 μm. Tin fine lines with 500×400 μm or 600×200 μm sizes were formed. Electric currents with current density as high as 2×10⁴ A/cm² were passed through the Sri fine lines at different temperatures. Optical microscopy and scanning electron microscopy analyses were performed to observe the evolution of the surface microstructure. As a result of the high current density, the grain structure changed and surface became rough. The grain boundary was twisted by stress. Holes and hillocks were also discovered. Interestingly, we found that the hillocks were tilted. Temperature was found to enhance the electromigration effect.