Effect of the thickness of nickel film interlayer on direct‐bonded aluminum/alumina as substrate in high‐power devices

Abstract Aluminum (Al) was successfully bonded with alumina (Al 2 O 3 ) using Ni films of different thicknesses (3, 6, 12 μm) through electroplating and electroless plating processes after annealing at the relatively low melting point of Al. The microstructure, bonding area percentage, shear strength, and thermal conductivity of Al/Al 2 O 3 joints were evaluated using scanning electron microscopy, scanning acoustic tomography (SAT), the ISO 13124 test, and the laser flash method respectively. No reaction layer was found at the interface of the Al/Al 2 O 3 joint, and the Ni film diffused completely into Al to form an intermetallic compound, Al 3 Ni, in the Al foil. The amount and size of the Al 3 Ni phase in the Al foil increased gradually with the thickness of the Ni film. The samples with Ni deposited via electroplating had a higher shear stress and bonding area than the samples with Ni deposited via electroless plating. The Al/Al 2 O 3 specimen with a 3‐μm‐thick Ni film interlayer deposited using electroplating had the highest shear strength (50.6 MPa), thermal conductivity (39.45 W/mK), and bonding area percentage (~99.97%); therefore, specimens produced under these conditions were considered suitable for use as a substrate in high‐power devices.