A novel integrated approach to optimize copper wire bonding processes and manufacturing

Copper is nowadays replacing the traditional gold in wire bonding interconnections, due to lower cost, better thermal/electrical properties and reliability performances. The increased hardness of Cu imposes higher bonding force and ultrasonic power during the wire-bonding process, increasing the risk of stress-induced bondpad damage. The aim of the presented work has been the modeling and characterization of stress and deformations resulting from the ball-bonding phase in order to have a quantitative method able to optimize the process set-up and the manufacturing capabilities already at design level. A finite element model has been developed and benchmarked with experimental samples obtained by freezing the ball bonding process at different steps, on which the deformations occurred in the bonded copper ball and in the bondpad layers have been measured through Xe plasma focused ion beam (Plasma-FIB) cross sections.