Au-Ag Bonding for 3D Stacked Package

摘要

Bipolar transistor is widely applied in the field of power electronics. However, there still exist many difficulties to manufacture high voltage Bipolar transistor nowadays. One of the approaches that can improve the withstand voltage of the Bipolar transistor is to stack multiple low-withstand voltage bipolar chips. SiC Schottky diode is bipolar transistor with aluminum electrode as anode and silver electrode as cathode. The purpose of this work was to realize the 3D die stacking by Au-Ag thermocompression bonding of two chips with the same electrode structure as SiC Schottky Diode. Gold stud bumps were made on the aluminum electrode by thermosonic bonding. Two chips were stacked together by Au-Ag thermocompression bonding. Different bonding parameters and annealing conditions were evaluated. Experiment results showed that increasing bonding temperature or annealing duration could improve the bonding quality. The Au-Ag bonding with 15N bond load at 250°C for 20 minutes followed by nitrogen annealing at 160°C for 30 minutes exhibited a successful bonding performance. The Au-Ag bonding interface was analyzed by SEM (scanning electron microscope) and EDX (energy dispersive x-ray spectroscope). Continuous alloy compositions were observed by atomic diffusion between gold and silver.