Electrical Transition Interfaces at Aluminum Terminations

The electrical connection between an aluminum (Al) conductor and a contact surface of some other metal-transition interface-has under certain circumstances exhibited contact resistance characteristics that are different from those between two Al members. Because these characteristics change the quality of the conducting path, it is essential that they be controlled. Electrical test interfaces include nonplated Al bus and zig-zag wire grids for AI-Cu, AI-Ni, and AI-Sn transitions with various contact surface treatments of the nonplated Al bus. The mode of interference between bus and wire is such that entrapment of the interface is minimal. Contact surface treatments of the Al in assembly include a) abrasion and coating with Alcoa No. 2 electrical joint compound, b) abrasion only, and c) no surface treatment. Contact resistance measurements after application of clamping force and with exposure to elevated temperatures in an oven permit evaluation of the several transitions in their ability to disrupt and collapse the interfaces as well as to protect the elemental contacts against destruction from thermal excursions. The AI-Sn interfaces with platings of 3-, 8-, and 13-µm thickness show the virtue of the thinnest plating in establishing and maintaining low-contact resistance. The AI-Ni interfaces show the ability of Ni to maintain good fixity with a nonplated Al surface. Contact resistances from twisted-pair tests are also given.