Intermetallic phase transformations in Au-Al wire bonds

This paper describes the crystallochemical mechanisms that underpin the migration of nano-size alumina, intermetallic growth and phase transformations in Au-Al wire bonds during annealing from 175 degrees C to 250 degrees C by utilizing high-resolution transmission electron microscopy (HRTEM). Alumina, encapsulated within the Au-Al intermetallic compounds (IMCs), migrates towards the Au ball during annealing, with Au diffusion into the Al pad. The sequence of Au-Al IMC phase development during annealing was investigated. Initially. Au(8)Al(3) appears as a third phase between the Au(4)Al and AuAl(2) layers that form during bonding, and gradually becomes the dominant compound. Both AuAl(2) and Au(8)Al(3) are transformed into the Au-rich alloyAu(4)Al when Al is completely consumed, and this is the terminal product. (C) 2011 Elsevier Ltd. All rights reserved.