Bonding of Al to Al2O3 via Al–Cu eutectic method

The Al oxidation layer in the manufactures of direct aluminum bonded Al2O3 substrates (DAB) has been a long-term trouble for industries. In this work we propose a new method for fabricating the DAB substrates with no requirement of high vacuum or active O2-getters. The new method comprises two stages: (i) Cu-film is bonded onto Al2O3 ceramic surface via DBC method; (ii) Al foil is joined to the DBC substrate by Al–Cu eutectic method at 600°C in pure N2 atmosphere. KF–AlF3 flux was used to disrupt the Al–oxide layer on the surface of Al foil. The wetting ability was significantly enhanced due to the diffusion of Cu into Al and the dissolving of Al. The final contact angle is achieved of 22.10°. Microstructure and composition of the interface between Al and Al2O3 substrate were analyzed. The XRD, SEM and EDS results show that two new phases Al2Cu and CuAlO2 were formed, leading to a strong bonding along the interface. The thermal cycling reliability and adhesion strength of DAB substrates were also evaluated. The results show that the DAB substrates can satisfy application requirements completely. [Display omitted] •A new method for fabricating the DAB substrates with no requirement of high vacuum or active O2-getters•Significant improvement in the wetting of aluminum was achieved by applying a coating of Cu on Al2O3 ceramic.•At relatively low temperature (600°C), the superficial Al-oxide film is disrupted by the treatment with KF–AlF3 flux.•Two new phases Al2Cu and CuAlO2 were formed at the interface leading to a strong bonding of DAB substrate.