Electromigration induced spontaneous Ag whisker growth in fine Ag-alloy bonding interconnects: Novel polarity effect

Ag-alloy wire has been recognized to be a good candidate for interconnect in light-emitting diode (LED) technology. This study employed fine Ag-alloy wires bonded on Al-Si pad to investigate their failure mechanism under current stressing of 8×104A/cm2 at ambient temperature of 150°C and 175°C, respectively. We report a novel polarity effect that the spontaneous whisker growth of Ag near bonded area only happens when electrons flowed from Al to Ag, while surface of bond joints remains intact with electrons flowed from Ag to Al, suggesting that the nucleation and growth of Ag whisker is strongly affected by the direction of electron flow. We proposed that the different behaviors on the whisker growth is because compressive stress caused by current crowding effect only builds up with electrons flowed from Al to Ag.