Cu wire bond microstructure analysis and failure mechanism

In this study, copper wire bonding samples were aged at 205 °C in air from 0 h to 2000 h. It was found that the bonding of a Cu wire and an Al pad formed Cu₉Al₄, CuAl, and CuAl₂ intermetallic compounds, and an initial crack was formed by the ultrasonic squeeze effect during thermosonic wire bonding. The cracks grew towards the ball bond center with an increase in the aging time, and the Cl ions diffused through the crack into the ball center. This diffusion caused a corrosion reaction between the Cl ions and the Cu-Al intermetallic phases, which in turn caused copper wire bonding damage.