Direct bonding of aluminum to alumina using a nickel interlayer for power electronics applications

Three films of Ni with thicknesses of 100, 300, and 500 ​nm were deposited on an Al2O3 base and direct bonded with Al to form high-power electronic substrates for comparison. The microstructures of Al/Al2O3 joints were evaluated using a scanning electron microscope (SEM) and transmission electron microscope (TEM) equipped with an energy dispersive spectrometer. No reaction layer was found at the interface between Al and Al2O3, and the Ni film dissolved in the Al foil and reacted with Al to form a eutectic liquid phase near the interface to wet and join with the Al2O3 base. An Al3Ni intermetallic compound was formed in the Al substrate because of Ni precipitation, which reacted with Al at its grain boundaries. The bonding area percentage, shear strength, and thermal conductivity for Al and Al2O3 were evaluated using scanning acoustic tomography (SAT), ISO 13124 shear strength test, and the laser flash method, respectively. The Al/Al2O3 specimen deposited with the 500-nm Ni film had the highest shear strength (31.5 ​MPa), thermal conductivity (37.8 ​W/mK), and bonding area percentage (~99.68%).