Inhibition of the formation of aluminum–copper intermetallic compounds in direct-bonded aluminum–copper ceramic substrates by using a silver metallic interlayer

A silver metallic interlayer was inserted into a direct-bonded aluminum–copper (DBAC) substrate to inhibit the formation of aluminum–copper intermetallic compounds (IMCs) in the substrate. The Ag caused the dissolution of small quantities of Al and Cu to form a Ag(Al, Cu) metallic layer, which exhibited lower hardness (1.4 ± 0.2 GPa) and a lower elastic modulus (71.7 ± 12.8 GPa) than did Al–Cu IMCs (hardness/elastic modulus: 10.4 ± 0.9 GPa and 193.9 ± 7.2 GPa for Al 4 Cu 9 , 10.6 ± 0.3 GPa and 171.2 ± 10.7 GPa for Al–Cu, and 7.6 ± 1.5 GPa and 121.0 ± 8.4 GPa for Al 2 Cu, respectively). Moreover, the Ag(Al, Cu layer was able to withstand high stress caused by the coefficient of thermal expansion mismatch between Al, Ag, and Cu; thus, this layer prevented crack formation at the Al–Cu bonding interface. The shear strength of the Al–Cu bonding interface was originally 13.3 ± 3.4 MPa. This value then increased to 26.3 ± 3.6 MPa when a Ag metallic interlayer was inserted, and the shear strength was maintained at 21.9 ± 1.1 MPa during 500 thermal cycles between − 50 and 150 °C. At room temperature, the thermal conductivity of DBAC with a Ag metallic layer (280 W/mK) was higher than that of direct-bonded aluminum (233 W/mK) and DBAC without a Ag metallic layer (276 W/mK) because of the high thermal conductivity of Ag and the absence of Al–Cu IMCs in the DBAC with a Ag metallic layer. Graphical abstract