Abstract
The recent growing focus on higher packaging densities, better performance, and smaller feature sizes in consumer electronic products has simulated greater development of three dimensional integrated circuits (3D IC) package. In this study, we report the microstructural evolution of Pb-free micro-bump under a temperature gradient in the 3D IC samples. Fast dissolution of Ni UBM thin-film near the hot end and the growth of Ni3Sn4 intermetallic compound on the cold side were observed, indicating that temperature gradient has driven Ni moved to the cold end. Additionally, void formation was observed at the hot side, and we propose the rapid diffusivity of interstitial Ni is responsible for the void formation. The molar heat of transport (Q*) of Ni in Sn is calculated. Due to recent greater development of 3D ICs, temperature-gradient induced fast dissolution of interstitial Ni could significantly impact the reliability of the micro-bumps in the 3D IC package.