Aluminum to Aluminum bonding at room temperature

In this work we show that high density and very low pitches face to face Aluminum/Aluminum cold bonding is feasible when using Aluminum coated micro-tubes inserted into Aluminum pads. First, mechanical simulations by FEM show that the insertion pressure felt on the top edge of the Aluminum coated micro-tube is sufficient to break native aluminum oxide present at the interface and also insure the large plastic deformation of aluminum terminations necessary for good electrical and mechanical contact at the joint. Then an electrical demonstrator with over 10⁶ connections at a 10 μm pitch is designed, assembled and characterized: the resistance values of the Al/Al bonds prove to be similar to those obtained with Au/Al bonds. Ion Beam cross-sections associated with SEM microscopy is used to characterize the morphology of the interface and shows that seamless Al/Al interfaces can be obtained if certain conditions are fulfilled. Finally the fundamentals of the cold insertion bonding process are discussed and a relationship established with “cold roll bonding” mechanisms, it is shown that the two techniques present some similarities related to very large plastic deformations of bonded materials. This helps us to develop a bonding theory to thoroughly explain the mechanism of the Aluminum/Aluminum bonds formation during the insertion process, as well as its kinematic scenario.