Environmental Effects on Structural, Mechanical and Electrical Properties of Al/Al Interfaces Joined at Room Temperature

Aluminum/aluminum joints were prepared by means of the surface activation room temperature bonding technique in following different vacuum conditions. The relationship among microstructure, mechanical property and electrical property of the interface was clarified. (1) When surfaces are activated by argon beam sputtering in ultra-high vacuum (10−9 Pa), indeally clean surfaces are adhered in the atomic scale. (2) In a vacuum of 10−5 Pa, surfaces are attacked by residual gases such as H2O during argon beam sputtering. A crystalline altered layer in about 5 nm thickness is formed on the surface before bonding. The layer affects the interfacial microstructure, but the tensile strength is more than 100 MPa and the interface electrical resistivity is as low as less than 10−12 Ω·m2 in such a joint. (3) When the activated surface is exposed before joining, the bonding properties deteriorated due to the surface contamination of a residual gas. The interface is fully covered with an intermediate amorphous layer of a few nm in thickness in a specimen exposed for 7.3 ks in a vacuum of 2.7×10−5 Pa. As a result, the interface resistivity increased drastically (∼10−10 Ω·m2) and the tensile strength decreased to 50 MPa. It should be emphersized, however, that a macroscopic bonding is obtained in the Al/Al system in such a contaminated condition suggesting that a clean and/or atomically activated surface is not necessarily essential to the mechanism of the room temperature bonding.