Accelerated lifetime measurements of Cu-Al ball bonded interconnects

Static shear tests are the state of the art testing methods for assessment of reliability and bonding strength of thermosonic ball bonds in microelectronic devices. As such interconnects are subjected to elevated temperatures and thermo-mechanically induced cyclic stresses, a degradation at the interface is expected that affects the reliability of ball bonded interconnects leading to subsequent fatigue failure. In this study a new accelerated mechanical fatigue testing method is proposed for determination of lifetime of miniaturized Cu-Al ball bonded interconnects. Lifetime is determined by subjecting interconnects to cyclic shear stresses at preset shear stress amplitudes. The effect of microstructural evolution to high temperature storage on bonding strength and lifetime of Cu-Al ball bonds was evaluated by means of static shear tests and the new fatigue testing method. The response of thermosonic ball bonds to static and cyclic loading was compared and discussed considering the fracture surface analysis of interconnects in as-bonded and aged conditions.