Interface Structure and Bond Strength of Copper‐Bonded Alumina Substrates

Copper‐bonded alumina substrates with different interface structures were studied to elucidate their effect on the bond strength and the resistance to hydrogen embrittlement and thermal cracking. The substrates were made by bonding copper either directly to alumina using Cu‐O eutectic reaction or indirectly with an interlayer of cuprous aluminate between the metal and the ceramic. The substrate with the aluminate interlayer shows somewhat lower bond strength, still adequate for its use, than the directly bonded substrate. However, the substrate with the aluminate layer has greater resistance to hydrogen embrittlement and thermal cracking. The cause of such improvement is ascribed to the porosity of the aluminate layer and the compressive stress induced in alumina.