Nanoscale analysis of ultrasonic wedge bond interface by using high-resolution transmission electron microscopy

In this paper, the bond interface of Al-1 wt.%Si wire bonded on Au/Ni/Cu pad at atmosphere temperature was analyzed by using high resolution transmission electron microscopy. Nano-scale characteristics at bond interface indicated that elemental aluminum diffusing into gold layer was with the feature of step-level periodicity. Due to exceeding solid solubility limit, intermediate Au₈Al₃ phase penetrated among the Al-Au solid solutions. The diffusion distance was not more than 100 nm analyzed by energy X-ray dispersive spectrum. This process controlled by solid diffusion reaction was realized by the rapid and periodic ultrasonic vibration according to the theoretical calculation based on the Fickpsilas Law and the observation of the deformation twins among the bond wire and within the interfacial diffusion layer.