Thermosonic ball bonding is a metallurgical process that until recently was rarely the subject of metallurgical analysis. However, in recent years greater focus has been given to the materials science of thermosonic ball-wedge bonding in an attempt to better control and advance its application as an interconnect technology in advanced packaging. As with most materials processes, establishing a scientific understanding of the process requires knowledge from various sub-disciplines of physical science. This article briefly reviews selected aspects of the materials science of ball bonding, focussing on 1st and 2nd bond formation and intermetallic growth. (C) 2009 Elsevier Ltd. All rights reserved.