The Current Induced Mass Transformation of Ag Alloy Wire Bonded Led Chip

Abstract

The high input and output (I/O) data exchange and the continuous improvement of power density increase the risk of bonding interface performance degradation and electromigration (EM) failure during the electrical transmission, and will also lead to polarity differences in interconnection structures. In this study, the polarity effect of EM in the chip-side Ag-Al system is described to reveal the evolution of bonding interfaces under high current density. The results show that dendritic growth of Ag appears at the anode of the chip after 1000 hours of EM exposure, likely due to the electrochemical migration of Ag ions caused by bias voltage. At the bond on the chip side, Ag whiskers are formed due to compressive stress. The polarity effect induced by current significantly affects material migration, growth, and evolution of intermetallic compound (IMC) at the interface. After 3000 hours of EM, the IMC layer at the anode interface and the edge of the micro joint is thickened synchronously, which is quite different from the cathode. After long-term EM, the interface compound is dominated by Ag2Al phase. The bonding wire becomes thicker at the chip side, which is related to the higher atomic flux at the chip side. The mechanical properties of the bonds caused by EM increase first and then decrease with the extension of migration time. The fracture failure mode of the micro-joint has shifted from a single neck fracture to bond delamination. This is related to the increased material transport rate caused by current, heat, and humidity.

Keywords: Ag wire bonding, Ag-Al, Electromigration, Polarity effect, Mechanical property