Tuning the microstructure and enhancing the mechanical properties of Au-20Sn/Au/Ni(P)/Kovar joint by ultrasonic-assisted soldering method

Improving the reliability of the solder joint has been the recent research focus in the electronic packaging field due to the increasing degree of integration in the electronic devices. During the reflow soldering process, when the local component is heterogeneous, the coarse structure of the solder joint is easy to grow, which deteriorates the performance of the solder joint. In this study, Au-20Sn/Au/Ni(P)/Kovar joints were prepared using ultrasonic-assisted reflow soldering process. Ultrasonication during reflow improved the wettability and shear strength between the Au-20Sn solder and Kovar substrate. The applied ultrasound can break the primary Au5Sn grain and refine the eutectic microstructure through acoustic cavitation. Meanwhile, ultrasound induced the formation of a new intermetallic compound (IMC) layer that was identified as Ni3P (ca 120 nm), which inhibited the diffusion of Ni from substrate into the solder matrix. The mechanical properties of Au-20Sn/Au/Ni(P)/Kovar joint treated with 80 W ultrasonic vibration (USV) increased by 46.94% as compared to the control sample. The current study provides a new strategy for high-performance packaging in electronic devices in extreme environments.